PROBING THE SURFACE ACTIVITY OF ACTIVATED CARBON

PROBING THE SURFACE ACTIVITY OF ACTIVATED

CARBON; OXIDATION OF CYCLOALKANES IN THE

PROTOCOL OF GREEN CHEMISTRY

Submitted by

Ms. Razia

DEPARTMENT OF CHEMISTRY

UNIVERSITY OF MALAKAND

2018

PROBING THE SURFACE ACTIVITY OF ACTIVATED

CARBON; OXIDATION OF CYCLOALKANES IN THE

PROTOCOL OF GREEN CHEMISTRY

A dissertation submitted to the Department of Chemistry, University of

Malakand, in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY IN CHEMISTRY

Submitted by

Ms. Razia

DEPARTMENT OF CHEMISTRY

UNIVERSITY OF MALAKAND,

SESSION 2013

Dedicated to my Husband, Umer Dil Wazir,

my Parents and my lovely daughter, Eshaal

Umer. It would have never been possible to

complete my education if you were not there for

every single moment

i

ii

Acknowledgement

First, I would like to thank my supervisor Dr. Muhammad Sadiq for giving me the opportunity

to work in his lab under his kind supervision. I am very thankful to him for his guidance and

support throughout the course of this research.

I am grateful to Dean of Sciences, Professor Rashid Ahmad for his teachings and

guidance during my course work and write up.

I am thankful to Professor Manzoor Ahmad, Chairman, Department of Chemistry, for

facilitation and encouragement.

I wish to thank the Faculty of Physical Chemistry, Professor Sultan Alam and Professor

Najeeb Ur Rahman for their guidance and support.

I am thankful to all the Faculty members of Department of Chemistry for their teachings,

guidance, and help during my doctoral studies, especial thanks to Dr. Mumtaz Ali, Coordinator

M. Phil/ PhD for his guidance in the writing and submission of thesis.

I greatly acknowledge the financial support from Higher Education Commission of

Pakistan under project number 20-1897/NRPU/R&D/HEC/116806 for two years.

I also acknowledge the financial support of Higher Education Commission of Pakistan

under IRSIP to pursue research in USA for six months.

I am grateful to distinguished Professor Abraham Clearfield for allowing me to work in

his lab for an exchange program. I especially appreciate the financial support from Dr. Clearfield

during my extended period at Texas A&M University in College Station, USA under project

#213510-00071, ZS Pharma.

Further, I appreciate the staff of Centralized Resources Laboratory and NCE in Physical

Chemistry, Peshawar, for characterization of the catalysts.

I appreciate the sincere cooperation of my lab fellows throughout my studies.

Razia

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Abstract

Cycloalkanes/cyclohexene, benzyl alcohol oxidation and Heck reaction have been investigated in

the protocol of green chemistry using variety of catalysts such as activated carbon (AC),

MOF/ZrP, Pd/Carbon dots in a self-designed batch type glass reactor.

The activated carbons from peanut shells, corn cobs, spent tea leaves (STL) and olive pits

have been prepared by different procedures and characterized by XRD, SEM, FTIR, TGA/DTA

and BET surface area and pore size analyzer. The AC from peanut shells show good catalytic

activity for cyclohexane oxidation with oxygen and air, in the absence/presence of a base. While

AC from corn cobs and STL are inactive under any reaction conditions. The oxidation of

cyclohexane occurred on the quinonic functional groups of AC present on the surface of AC

from peanut shells. The catalytic activity of AC was also screened for oxidation of benzyl

alcohol to benzaldehyde with air at mild reaction conditions.

Similarly, AC from olive pits was used for adsorptive removal of toluidine blue from

aqueous solution. The removal of toluidine by AC followed Temkin isotherm and first order

kinetics where 83% dye was removed from the solution.

Carbon dots were synthesized by a green route and Pd nanocrystals (nanocubes and

octahedrons) were used for quenching of carbon dots. The green fluorescence of carbon dots

vanished with quenching as Pd is a best quencher having 4D8 configuration. The uptake of

nanooctahedrons was more favorable in comparison with nanocubes. Pd/C-dots were used for

catalyzing Heck reaction between aryl iodide and styrene. Pd nanooctahedrons/C-dots shows

71% yield in 4 hours.

Layer by layer HKUST-1 supported on zirconium phosphate has been used as catalyst for

oxidation of cyclohexene in solvent free conditions. The conversion and selectivity towards

products changed with the number of layers of HKUST-1 on ZrP. 92% conversion was observed

with less than 1% by-products. The catalyst was found selective for allylic oxidation with

molecular oxygen.

Keywords: Activated Carbon, cycloalkane, solvent free system, batch reactor

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CONTENTS

Certificate ....................................................................................... Error! Bookmark not defined.

Acknowledgement .......................................................................................................................... ii

Abstract .......................................................................................................................................... iii

Contents……………..……………………………………………………………………………iv

List of Figures…………………………………………………………………………………...viii

List of Tables……………………………………………………………………………………..xi

List of Schemes..…………………………………………………………………………………xi

List of Abbreviations………………………………………………………………………….... xii

1. Introduction ............................................................................................................................... 1

1.1 Aims and Objectives ............................................................................................................. 1

1.1.1 Oxidation of Cycloalkane ............................................................................................... 2

1.1.2 Oxidation of Alcohol ...................................................................................................... 2

1.1.3 Adsorptive removal of toluidine blue ............................................................................. 3

1.1.4 Carbon Dots for the adsorption of Pd nanocrystals ........................................................ 3

1.1.5 Pd/Carbon Dots for Heck reaction .................................................................................. 4

1.1.6 Metal-organic frameworks for oxidation of cyclohexene .............................................. 6

2. LITERATURE REVIEW ........................................................................................................ 8

3. EXPERIMENTAL .................................................................................................................. 17

3.1 Materials .............................................................................................................................. 17

3.1.1 Chemicals ..................................................................................................................... 17

3.1.2 Gases ............................................................................................................................. 17

3.2 Catalysts Preparation ........................................................................................................... 19

3.2.1 Activated Carbon (AC1a, b, and c) .............................................................................. 19

3.2.2 Catalytic Test of AC (Ia, b and c) ................................................................................. 19

3.3 Activated Carbon from Peanut shells (AC II) ..................................................................... 20

v

3.3.1 Catalytic Test of AC II ................................................................................................. 20

3.4 Activated Carbon from Olive stones (AC III) ..................................................................... 20

3.4.1 Batch Study................................................................................................................... 21

3.4.2 Fixed Bed Column Study ............................................................................................. 21

3.5 Synthesis of Zirconium Phosphate by Reflux Method........................................................ 21

3.5.1 Sodium Ion Exchange ................................................................................................... 21

3.5.2 Synthesis of HKUST-1 on the Surface of ZrP ............................................................. 22

3.6 Preparation of Carbon Dots ............................................................................................ 22

3.7 Palladium Nano-Crystals Preparation ................................................................................. 22

3.7.1 Reagent A for octahedral crystals ................................................................................. 22

3.7.2 Reagent A for cubic crystals ......................................................................................... 23

3.7.3 Reagent B ..................................................................................................................... 23

3.8 Preparation of Pd/Carbon Dots ........................................................................................... 23

3.9 Characterization of the Samples .......................................................................................... 23

3.10 Experimental Set-up for the screening of catalysts ........................................................... 24

3.11 Analysis of Reaction Mixture ........................................................................................... 25

3.12 Gravimetric Method .......................................................................................................... 25

3.13. Calculations...................................................................................................................... 26

3.14 Gas Chromatographic Method .......................................................................................... 26

4. Results & Discussion: ............................................................................................................. 29

4.1 Oxidation of Cycloalkane to Alcohol and Ketone .............................................................. 29

4.1.1. Characterization of the Samples. ................................................................................. 29

4.1.2 Optimization of reaction parameters ............................................................................ 35

4.1.3 Effect of the reaction time ............................................................................................ 35

4.1.4. Effect of Partial Pressure and flow of Oxygen ............................................................ 35

vi

4.1.5. Effect of Temperature .................................................................................................. 35

4.1.6. Effect of catalyst loading ............................................................................................. 35

4.1.7. Effect of Stirring .......................................................................................................... 37

4.1.8. Catalytic activity of the catalyst .................................................................................. 37

4.1.9. Activation energy ........................................................................................................ 40

4.1.10. Recycling of catalyst ................................................................................................. 43

4.1.11. Oxidation of other Cycloalkanes ............................................................................... 43

4.2. Results and Discussion: Oxidation of Alcohol to Aldehyde by AC II............................... 45

4.2.1. Characterization of the catalyst (AC II) ...................................................................... 45

4.2.2. Oxidation of Alcohol ................................................................................................... 50

4.2.3. Optimization of Reaction Conditions .......................................................................... 50

4.3 Results and Discussion: Adsorption of Toluidine Blue by Activated Carbon from Olive

Pits (AC III) ............................................................................................................................... 58

4.3.1. Characterization of AC III ........................................................................................... 58

4.3.2 Effect of various parameters on percent removal of Toluidine Blue ........................... 61

4.3.3. Thermodynamic parameters ........................................................................................ 65

4.3.4. Adsorption kinetics ...................................................................................................... 65

4.3.5. Adsorption Isotherm .................................................................................................... 67

4.3.6. Fixed bed column study ............................................................................................... 68

4.3.7. Fractal analysis ............................................................................................................ 69

4.4. Results and Discussion: Carbon Dots Synthesis, Quenching and Catalysis ...................... 71

4.4.1. Fluorescence Spectra of Carbon Dots ......................................................................... 71

4.4.2. Effect of time of autoclave on the formation of carbon dots ....................................... 71

4.4.3. Effect of time on the stability of carbon dots .............................................................. 71

4.4.4. Effect of pH on the formation of carbon dots .............................................................. 75

vii

4.4.5. Effect of concentration of carbon dots on their yield .................................................. 77

4.4.6. Characterization of Pd nanocrystals ............................................................................ 79

4.4.7. Palladium nanocrystals Uptake by Carbon Dots ......................................................... 82

4.4.8. Heck Reaction .............................................................................................................. 82

4.5. Results and Discussion: Oxidation of Cyclohexene by Metal-Organic Frameworks Hybrid

................................................................................................................................................... 87

4.5.1. Characterization of MOF/ZrP ...................................................................................... 87

4.5.2. DFT Study of HKUST-1 ............................................................................................. 94

4.5.3. Oxidation of Cyclohexene ........................................................................................... 96

Conclusions .................................................................................................................................. 99

REFERENCES .......................................................................................................................... 101

List of Publications

viii

List of Figures

Figure 3. 1: Experimental set up used for oxidation reaction of Cyclohexane. ........................... 25

Figure 3. 2: Calibration curve for alcohol/ketone in cyclohexane ............................................... 28

Figure 4. 1: SEM images of the (AC Ia) at different magnifications. (a) and (b) represent the

magnified areas marked in large image. ....................................................................................... 30

Figure 4. 2: SEM images of the (AC Ib) and (AC Ic). ................................................................ 30

Figure 4. 3: Elemental analysis of (AC I a,b,c).. ......................................................................... 31

Figure 4. 4: XRD diffraction pattern of (AC I a,b,c). .................................................................. 31

Figure 4. 5: Thermogram of (AC Ia) obtained at T=25-1000°C. ................................................ 33

Figure 4. 6: FTIR spectra of (a) carbonized carbon, (b) activated carbon (H2O2), and (c)

thermally activated carbon. ........................................................................................................... 34

Figure 4. 7: Reaction parameters (a) time, (b) partial pressure of oxygen, (c) flow of oxygen, (d)

temperature, (e) catalyst loading, and (f) stirring effect ............................................................... 36

Figure 4. 8: (a) Alcohol and Ketone formation as a function of oxygen. And (b) Cycloalkane to

Alcohol and Ketone conversion in oxygen, nitrogen, air, and base. ............................................ 38

Figure 4. 9: Arrhenius plot of AC-catalyzed conversion of CH to alcohol and ketone .............. 44

Figure 4. 10: Recycling of AC for cyclohexane to KA oil. ......................................................... 44

Figure 4. 11: SEM images of AC II impregnated with (a) 10% H3PO4 (b) 15% H3PO4 (c) 20%

H3PO4 (d) 25% H3PO4 (e) 30% H3PO4 (f) 35% H3PO4 (g) 40% H3PO4 at magnification of 500.46

Figure 4. 12: XRD Pattern of (AC II) impregnated with 10% H3PO4 ......................................... 47

Figure 4. 13: FTIR of (AC II) impregnated with 10% and 15% acid .......................................... 47

Figure 4. 14: Plot of ln a/(a-x) vs time (hours), oxidation of benzyl alcohol into benzaldehyde 53

Figure 4. 15: Plot of mol % Conversion vs Time (hours), Oxidation of ROH to RCHO. .......... 54

Figure 4. 16: Effect of temperature on the conversion of ROH to RCHO. ................................. 56

Figure 4. 17: Arrhenius plot for activation energy. ..................................................................... 56

Figure 4. 18: Plot for particle size vs % conversion .................................................................... 57

Figure 4. 19: SEM images of AC III ........................................................................................... 59

Figure 4. 20: XRD pattern of AC III ........................................................................................... 60

Figure 4. 21: FTIR spectra of (AC III) ........................................................................................ 60

ix

Figure 4. 22: Influence of pH on % Removal of Toluidine Blue by ACIII. ................................ 63

Figure 4. 23: Effect of amount of AC III on TB removal ............................................................ 63

Figure 4. 24: Adsorption of TB at different concentrations ........................................................ 64

Figure 4. 25: Adsorption of TB as a function of Temperature .................................................... 64

Figure 4. 26 (a): Pseudo-first-order kinetics for TB adsorption on ACIII .................................. 66

Figure 4. 26 (b): Pseudo-second- order kinetics for TB adsorption on ACIII…..……...……… 66

Figure 4. 27: Plot for intraparticle diffusion of TB ………………………………..…………. 67

Figure 4. 28: (a) Langmuir Adsorption Isotherm (b) Freundlich Adsorption Isotherm (c) Temkin

Adsorption Isotherm (d) Fractal analysis of AC........................................................................... 70

Figure 4. 29: Fluorescence Spectra of Carbon Dots. ................................................................... 73

Figure 4. 30: Effect of time on the stability of Carbon dots ........................................................ 74

Figure 4. 31: Effect of pH on the fluorescence intensity of Carbon dots .................................... 76

Figure 4. 32: Effect of concentration of carbon dots on fluorescence intensity (linearity study) 78

Figure 4. 33: TEM images of octahedral nanocrystal of Pd with scale bar: (a) 50 nm and (b)100

nm. ................................................................................................................................................ 79

Figure 4. 34: TEM images of Pd nanocubes with scale bar: (a) 50 nm and (b)100 nm. ............. 80

Figure 4. 35: XRD diffraction peaks of octahedral nanocrystals of Pd. ...................................... 80

Figure 4. 36: XRD diffraction peaks of Pd nanocubes. ............................................................... 81

Figure 4. 37 (a): Adsorptive quenching of Carbon Dots prepared at 5 h autoclave time ............ 83

Figure 4. 37 (b): Adsorptive quenching of Carbon Dots prepared at 10 h autoclave time......… 83

Figure 4. 37 (c): Adsorptive quenching of Carbon Dots prepared at 15 h autoclave time…..….84

Figure 4. 38: Heck reaction catalyzed by Pd nanocrystals/CDs .................................................. 85

Figure 4. 39: XRD pattern of ZrP amd MOF/ZrP with 10 layers ................................................ 88

Figure 4. 40: SEM images of ZrP, 2 Layers of MOF/ZrP, 4 Layers of MOF/ZrP and 6 Layers of

MOF/ZrP ....................................................................................................................................... 89

Figure 4. 41: (I) TGA of ZrP and MOF/ZrP (II) FTIR spectrum of MOF/ZrP (III) Surface area

of ZrP and different layers of MOF/ZrP (IV) Pore Volume of ZrP and different layers of

MOF/ZrP ....................................................................................................................................... 90

Figure 4. 42: N2 Adsorption/Desorption isotherm at 77 K for MOF/ZrP with 2, 4, 6 and 10

Layers of MOF .............................................................................................................................. 93

x

Figure 4. 43: Structure of HKUST-1 ........................................................................................... 94

Figure 4. 44: Electronic band structure of the HKUST-1 ............................................................ 95

Figure 4. 45: Electron charge densities of the HKUST-1 in (100) and in (110) crystallographic

directions ....................................................................................................................................... 96

Figure 4. 46: Conversion (%) and product distribution (%) with different number of MOF layers

on ZrP............................................................................................................................................ 98

xi

List of Tables

Table 3. 1: Chemicals List used in present study……..…………………………………………18

Table 4. 1: CH conversion at different parameters ...................................................................... 38

Table 4. 2: AC-catalyzed organic substrates, with productivity and reaction conditions ............ 42

Table 4. 3: Surface functional groups (AC II) ............................................................................. 49

Table 4. 4: Fluorescence Spectra of Carbon dots ......................................................................... 72

Table 4. 5: Effect of autoclave time on the fluorescence intensity of Carbon Dots .................... 74

Table 4. 6: Effect of pH on the fluorescence intensity of Carbon dots ........................................ 76

Table 4. 7: Effect of concentration of Carbon dots on the fluorescence intensity ....................... 77

Table 4. 8: Palladium catalyzed Heck reactions .......................................................................... 86

Table 4. 9: Surface area of MOF/ZrP with different number of Layers ...................................... 92

Table 4. 10: Oxidation of Cyclohexene reported in Literature and results from current study…98

List of Schemes

Scheme 4.1: Proposed mechanism for oxidation of CH with quinonic group of AC…………...41

Scheme 4.2: Oxidation of benzyl alcohol to benzaldehyde……………………………………..50

Scheme 4.3: Oxidation of benzyl alcohol to benzaldehyde……………………………………..51

Scheme 4.4: Oxidation of cyclohexene…………………………………………………………97

xii

List of Abbreviations

AC Activated Carbon

MOF Metal-Organic Frameworks

Pd Palladium

STL Spent tea leaves

XRD X-ray Diffractometry

SEM Scanning Electron Microscopy

FTIR Fourier Transform Infrared Spectroscopy

TGA Thermogravimetric Analysis

DTA Differential Thermal Analysis

BET Brunner Emmitt Teller

C-dots Carbon Dots

HKUST-1 Hong Kong University of Science and technology

DFT Density Functional Theory

CH Cyclohexane

BzOH Benzyl Alcohol

TB Toluidine blue

ZrP Zirconium Phosphate

KA Ketone/Alcohol

Conv Conversion

FI Fluorescence Intensity

NMP N-Methyl-2-pyrrolidone

DMF Dimethylformamide

xiii

SWCNTs Single Walled Carbon Nanotubes

MWCNTs Multi Walled Carbon Nanotubes

BTC Benzene tricarboxylate

C Carbon

PVP Polyvinyl Pyrrolidone

POM Polyoxometalate

AA Adipic Acid

WAO Wet Air Oxidation

GO Graphene oxide

N-GO Nitrogen-doped Graphene oxide

GAC Granular Activated Carbon

EG Ethylene Glycol

BTX Benzene Toluene Xylene

MB Methylene blue

HCN Hydrogen Cyanide

CAC Coffee grinded Activated Carbon

ACK Activated Carbon treated with K2CO3

CNCs Carbon Nanocoils

TBHP t-butyl hydroperoxide

FID Flame Ionization Detector

ROH Alcohol

RCHO Aldehyde

CHAPTER 01 INTRODUCTION

1

1. Introduction

Activated carbon is an interesting material, due to its physicochemical and electrochemical

properties and has been used in various industrial applications. It has also been used either a

catalyst support or a catalyst in catalysis. Depending on the raw materials and preparation

processes, these materials have different functional groups on their surface that are catalytically

active in different chemical reactions [1]. The oxygen containing functional groups on the

surface of activated carbons has been widely studied because these functional groups influence

the catalytic properties of activated carbons. These functional groups are introduced on the

surface of activated carbon during chemical activation process. The acidic, redox, hydrophilic

and catalytic properties of activated carbons are corelated to their several functional groups like

carboxylic, phenolic, pyrone, chromene, lactone and ether etc [2].

Activated carbon (AC) was first reported as an effective catalyst in the beginning of 19th

century [3]. In early nineteenth century, AC was commonly prepared by thermal activation

method using different agricultural raw materials, with the resulting ACs utilized as catalysts for

the degradation of hydrogen peroxide. The catalytic activity of AC for the decomposition of

hydrogen peroxide was considered good but activity only persisted for short durations. The most

probable reason for the loss of catalytic activity may be the deactivation of oxygenated groups on

the surface of activated carbon [4, 5]. This major issue relating to durability of AC has been

successfully addressed by researchers in recent decades. Through physical, physico-thermal,

chemical and chemo-thermal activation, AC can be tuned to show good catalytic activity [6] in

production of phosgene and sulphur halides, hydrogenation, polymerization, halogenation [7-9],

removal of SO2 and NOx [10, 11], and oxidation of benzyl alcohol [12]. This performance of AC

is generally attributed to its porosity, active sites, and high surface area. Thus, by controlling

these parameters, AC can be tuned as an effective catalyst for a selected organic transformation.

1.1 Aims and Objectives

The project was launched with following aims and objects:

Preparation of cost-effective catalysts

Investigation of surface properties and their influence on catalytic performance of the lab

prepared catalysts


2

Oxidation of cycloalkanes following the principles of green chemistry

Carbon Dots synthesis for selective adsorption of palladium nanocrystals

Palladium/Carbon Dots for Heck coupling reaction

Synthesis of metal-organic frameworks for oxidation of cycloalkanes and cycloalkene

1.1.1 Oxidation of Cycloalkane

The oxidation of cycloalkane to alcohol and ketone, especially six carbons containing

cyclic alkanes, is of immense importance due to their use as a starting material in the synthesis of

Nylon-6,6 and Nylon-6, as homogenizer and stabilizer in soaps and detergents [13, 14]. The

industrial scale production of alcohol/ketone was generally carried out in two steps, (a) the

uncatalyzed autoxidation of cyclohexane in the presence of oxygen to give an intermediate,

cyclohexyl hydroperoxide, (b) catalytic conversion of cyclohexyl hydroperoxide into

alcohol/ketone mixture using a homogeneous catalyst of cobalt. This process is limited due to

low cyclohexane conversion (3-4%), selectivity (60-70%) [15], high operating costs due to

recycling of unreacted CH, difficult separation of catalyst from reaction mixture, and use of large

quantity of a base (180 kg of NaOH) to produce a single kg of Alcohol/ketone mixture, which

generates approximately 1100 kg of alkaline waste [16]. Thus, to resolve the issue of

environmental safety and atom economy, a variety of heterogeneous catalysts are introduced for

the industrial scale production of alcohol/ketone.

1.1.2 Oxidation of Alcohol

The selective catalytic oxidation of alcohols to corresponding carbonyl products is one of

the fundamental methods in organic transformations in laboratory as well as in industry. The

corresponding carbonyl products are versatile intermediates in the production of fine chemicals.

Many processes using different stoichiometric reagents and catalytic methods have been

reported. Numerous oxidizing agents such as permanganate and dichromate have been frequently

used for this purpose, but these reagents have high cost and generates toxic waste [17]. Among

catalysts, different precious metals and their oxides supported on alumina and zirconia etc have

been reported to be efficient for oxidation of alcohols. But their high cost and leaching of active

species makes their use impractical for industries [18, 19]. Non-precious metal oxides, such as

cobalt oxide has also been investigated in oxidation processes but the catalytic properties of the


3

catalysts vary with different parameters such as preparation techniques, surface morphology,

surface area, particle size and shape [20].

Therefore, from an environmental point of view, ecofriendly oxidation systems using

clean and abundant oxidants such as O2, air, H2O2 and heterogeneous catalysts are highly desired.

The use of heterogeneous catalytic systems is preferred due to the ease of catalyst recovery and

recyclability.

1.1.3 Adsorptive removal of toluidine blue

Dyes have complex chemical structures consisting of large aromatic skeletons. On the

base of structure, dyes can be categorized into six classes, sulfur, azo, indigoid, anthraquinone,

triphenyl methane and phthalocyanine classes [21]. These dyes have been used in various

industries, such as paper, textiles, cosmetics, food, rubber, pulp, and lather, as methods of

coloring products [22]. Dyes have also been used in paper printing, colored photography and as

additives in petroleum products [23]. In fact, the global production of organic dyes is 450,000

tons/year, however approximately 15% of these dyes are lost in wastewater, making them

permanent part of industrial wastewater. Due to their complex structure, dyes are highly stable

and cannot be removed easily from wastewater. In the textile industry about 10–60% of the

losses of reactive dyes were recorded in wastewater. The existence of these dyes not only cause

the discoloration of water but also prevent sun light penetration into water which can stop

photosynthesis in water-based plants and inhibiting the growth of aquatic biota [24-27].

Furthermore, the toxicity of dyes includes carcinogenicity, cytotoxicity, hepatotoxicity,

microbial toxicity, mutagenicity, neurotoxicity and photodynamic toxicity [28, 29].

Thus, it is quite important to remove these chemicals from industrial wastewater before

discharging to the environment. For these applications, AC was commonly prepared from

agricultural residues such as husk, nut shells, wood, peat, saw dust, lignite, coal, bones, fruit pits,

charcoal, waste of paper mills and synthetic fibers. Thus, AC can be a useful material for the

removal of TB from aqueous solution.

1.1.4 Carbon Dots for the adsorption of Pd nanocrystals

Carbon dots (C-Dots), a new class of nano carbon materials with size less than 10 nm were

discovered with the electrophoretic purification of single walled carbon nanotubes [30]. Different


4

forms of carbon dots have been reported such as carbon quantum dots, carbon nanodots and

polymer dots. Carbon quantum dots are crystalline while other forms of C-Dots are amorphous

[31]. C-Dots have attracted attention of researchers due to their biocompatibility, low toxicity,

conductivity and photostability [32]. The most important property of C-Dots is their

photoluminescence and therefore they are referred as fluorescent carbons. Fluorescent carbon

dots have widely been used in bio-imaging, cell labeling and sensing, printing inks and solar

cells [33]. The photoluminescence can be quenched from carbon dots by either electron donor or

electron acceptor molecules in solution. Carbon dots can also be used as nanoprobes for sensitive

ion detection, drug delivery, therapeutics and catalysis due to many functional groups and

quenching efficiency [34, 35]. Carbon dots contain many carboxylic acid groups on their surface

thus enabling the functionalization of C-Dots with various organic, inorganic, polymeric and

biological species [36].

It is well known that the amount of metals, particle size, shape, preparation method and nature of

the support plays a crucial role in heterogeneous catalysis. The shape and size of supported

metals are greatly influenced by the support material due to different interactions. Similarly,

catalytic properties are influenced by the control of metal and support interactions [37].

Noble metal nanocrystals have gained enormous interest because it can provide a new way to

tune the electronic, magnetic, optical and catalytic properties of metals. Metal nanocrystals

reported to date are cubes, spheres, tetrahedron, octahedron and rods [38]. Among noble metals,

palladium has widely been investigated as active catalytic species in a variety of reactions

especially C-C bond formation. The catalytic activity depends upon the shape and size of the

nanocrystals. Pd nanocrystals have been prepared in cube, octahedron, decahedron, icosahedron,

plate, rod, and bar shapes enclosed by low index facets such as {111}, {100}, and {110} [39].

Carbon dots with green florescence have been synthesized and utilized for palladium adsorption.

The photoluminescence decreased with the uptake of palladium nanocrystals. Carbon Dots favor

the adsorption of cubic Pd nanocrystals as compared to octahedrons.

1.1.5 Palladium/Carbon Dots for Heck reaction

Heck reaction was introduced by Mizoroki and Heck independently in 1970. Heck reaction has

drawn much attention due to its chemo and regioselectivity and less toxicity. Heck reaction is


5

defined as arylation or vinylation of olefins. A large variety of olefins can be used such as

styrene, derivatives of acrylates and intramolecular C=C bonds. Initially aryl halides with

bromine and iodine were used but then more variants were introduced into this reaction such as

aromatic triflates, arylsilanols, aroyl halides and aryl anhydrides. Generally, less crowded

molecules are preferred in this reaction and often give trans products. Alkenes containing

electron withdrawing groups give β-arylated products. Alkenes with electron donating groups

give α- and β- arylated products. Triflates almost give α-arylated products and halides

predominantly give β-arylated products. Simple olefins lead to a mixture of alpha and beta

products [40].

This reaction has been carried out by homogeneous catalysts but its use on industrial scale is not

viable due to the contamination of products, poor stability and difficult separation from reaction

mixture. Ligands have been used for the stabilization of catalysts and to broaden their reactivity

still it is difficult to remove the catalyst completely [41]. To avoid the problem of leaching and

recovery, immobilization of ligand free palladium on carbon materials, metal oxides and zeolites

has been extensively explored in this area of research [42].

Different forms of carbon have been reported as carrier for metals and metal nanoparticles. It is

advantageous due to stability and ease of recovery of the catalyst after use. These supported

catalysts have been found to be highly efficient in numerous organic transformations [43].

Corma et al. [44] have explored Pd/SWCNTs for the Heck reaction of styrene and iodobenzene

in DMF at 150°C in the presence of NaAcO as a base. The catalyst showed high activity and

reaction was completed in 60 min where trans stilbene was the only product detected. Moussa et

al. [45] has reported Pd-partially reduced graphene oxide for the reaction of iodobenzene with

styrene and K2CO3 in water: ethanol solvent. The reaction was carried out under microwave

heating for 10 min at 180°C. Trans stilbene was produced with 95% purity at 100% conversion.

Zhu et al. [43] have reported Pd supported on carbon nanofibers for the Heck reaction of

bromobenzene with styrene in the presence of NMP and Na2CO3 at 120°C. 95% pure product

was achieved after 10 hours of reaction. Magnetic carbon nanocomposite supported Pd catalyst

(Pd/Fe2O3@C) has been reported for Heck reaction with 100% yield in 4 h at 120°C. DMF and

sodium bicarbonate were used in this reaction [46]. Deepa Dey et al. [47] have reported carbon


6

dot reduced palladium nanoparticles for the reaction of iodobenzene with styrene in the presence

of K2CO3 and water. 95% product was obtained in 12 h at 40°C. PVP was used as co stabilizer.

1.1.6 Metal-organic frameworks for oxidation of cyclohexene

MOFs, also known as metal coordination polymers are a new class of porous materials, formed

by connecting metal ions as nodes to multifunctional organic ligands such as di-, tri-, tetra- and

hexacarboxylates, imidazolates, dipyridyls as linkers [48, 49]. MOFs are novel inorganic-organic

materials combining organic and inorganic [50]. MOFs are highly crystalline having large

surface area (1000-15000 m2/g), and the low density (as low as 0.13 g/cm) [51-53].

The features of MOFs can be tuned by varying different parameters such as metal nodes and

organic linkers, solvents, as well as interactions among these metal nodes and linkers including

hydrogen bonding and π−π interactions [54]. The commonly used methodology is hydrothermal

or solvothermal, where generally the solutions of metal precursors and organic linkers are mixed

together [55-59]. A large variety of metals such as alkaline, alkaline earth, transition metals, and

rare earth elements have been successfully used in the synthesis of MOFs typically while in their

most stable oxidation states. The rigid organic linker is usually utilized in order to get the desired

MOFs. MOFs have applications in gas storage, purification, molecular sensing, drug delivery,

biomedicines, photoluminescence, molecular based magnetisms and photo catalysis [60-68].

Heterogeneous catalysis is one of the earliest proposed as well as one of the earliest

demonstrated applications for MOFs [69]. Currently, MOFs are used as solid catalysts for

liquid-phase organic reactions. Fujita et al. [70] have been reported one of the earliest examples

of cadmium-based MOF for the cyanosilylation of aldehydes with cyanotrimethylsilane which

resulted in 77% product. Xamena et al. [71] reported 2D, Pd(2-pymo)2]n MOF, that was able to

catalyze a variety of reactions such as oxidation, hydrogenation and C-C coupling reactions.

These examples were opportunistic catalysts. A second generation of MOF materials was

reported with designed frameworks such as [Cu3(btc)2] or HKUST-1 and MOF-199

([Cu2(btc)3/4]) which contain large cavities and exposed metal sites [72]. The HKUST-1

nanoparticles inside silica monoliths have been reported for continuous flow catalysis in liquid

phase Friedlander reaction. The CuBTC-MonoSil showed 2.5 times higher catalytic activity than

commercial Cu-BTC [73]. HKUST-1 has been investigated for the oxidation of trans-ferulic acid


7

into vanillin. The reactant was completely oxidized into vanillin in only 1 h with the yield of

95%. The unsaturated metal sites within the framework are responsible for the superb catalytic

activity of the catalyst [74]. Polyoxometalates supported MOF has been synthesized and utilized

as an acid catalyst for hydrolysis of esters in excess of water. MOF support enhanced the

catalytic activity of polyoxometalates (POM) by prohibiting the conglomeration and deactivation

of the POM [75]. Wang et al. [76] have reported Cu-CuFe2O4@HKUST-1 for the aerobic

oxidation of benzylic C-H bond. The reaction was carried out at 60°C where >99% fluorenone

product was obtained with a conversion of >99%. The catalyst is magnetically recoverable and

reused for ten times without any loss in activity.

CHAPTER 02 LITERATURE REVIEW

8

2. LITERATURE REVIEW

Peng et al. [77] have investigated carbon nanotubes (CNTs) for the liquid phase oxidation of

cyclohexane in a Parr autoclave in batch mode at 398 K and 1.5 MPa O2. The CNTs were

prepared by the chemical vapor deposition method in an NH3 atmosphere. Both undoped and N-

doped CNTs have been used as catalysts, with the activity of the N-doped catalyst being two

times higher than those of undoped CNTs. N-doped CNTs resulted in a 45.3% conversion with

59.7% adipic acid and 26.7% KA oil selectivity. The enhanced activity of N-doped CNTs has

been attributed to the π system of graphitic units as the radicals are much more stabilized by N-

containing complexes. This activity of N-doped CNTs is higher than supported gold and zeolite

catalysts reported while showing no loss in activity after 5 cycles.

Dai et al. [78] have tested the catalytic activity of Au and Co over AC in the aerobic oxidation of

cyclohexane in a stainless-steel autoclave reactor at 398 K and 1.5 MPa O2. The catalysts were

prepared by a chemical reduction method and a deposition precipitation method. Au/C resulted

in a 44.93% conversion with 54.85% adipic acid and 27.11% KA oil selectivity. Co/C showed

lower activity (35% conv, 46.18% AA, 34.81% KA oil) compared to Au/C but much higher

activity than AC alone (20.31% conv. 38.51% AA). The activity of metal supported AC catalysts

has been attributed to active metal species as well as the stability and structure properties of

activated carbon.

Chen et al. [79] have examined manganese and vanadium supported on different activated

carbons in the aerobic oxidation of benzyl alcohol. ACs have been treated with 0.5 M HNO3, 10

M H2O2 and oxygen for 3 h. Mn/AC-0.5 M HNO3 and V/AC resulted in a 67.3% and 92.6%

conversion respectively at 373 K and 10 mL/min flow of oxygen in a bath-type reactor with

toluene as the solvent. Benzaldehyde was the main product along with traces of benzoic acid

(less than 1%). The enhanced catalytic activity of the materials has been attributed to surface

properties of AC supports. Conversion of hydrophobic surfaces into hydrophilic and non-polar

into polar resulted in adsorption of BzOH and desorption of benzaldehyde. The interaction of the

metal precursor and support material can be influenced by the acidity or basicity of solutions.

The more basic the metal precursor solution than AC, the more favorable the ion interaction with

the support.


9

Zabihi et al. [80] have examined the activity of AC support for cobalt oxide and copper oxide in

the oxidation of toluene and cyclohexane in a tubular fixed bed flow reactor. Local almond

shells, walnut shells and apricot stones were used as precursors for activated carbon. Among Cu-

Co/AC (copper core and cobalt shell), Co-Cu/AC (cobalt core and copper shell) and Cu-Co/AC

(copper and cobalt mixed) catalysts, the catalytic activity of mixed metal oxides supported on

AC made from almond shells was higher for both the reactants. The %conversions for toluene

and cyclohexane were 96.34 and 93.11 respectively. The optimal temperature was 250°C for

more active catalyst Cu2-Co6/AC. CuO and CoO were detected on the surface of activated

carbon There was a slight difference in %conversion when toluene and cyclohexane were used in

mixture. The conversion was also slightly decreased by the presence of moisture although the

decrease was more pronounced for cyclohexane as H2O competed with VOCs molecules for

adsorption on the metal oxide.

Peng et al. [81] have investigated CNTs and N-doped CNTs for oxidation of cyclohexene in

Teflon-lined autoclave in batch mode. The catalysts were prepared by a chemical deposition

method. The catalytic activity of NCNTs was much higher than CNTs reaching 59% conversion

where five different products have been detected. Allylic oxidation with 52% selectivity was

more pronounced than epoxidation. Different nitrogen sources have been tested for nitrogen

content although the catalytic activity was enhanced by NH3. The selectivity altered with each

nitrogen source indicating that preparation conditions have a prominent role in oxidation

processes. The activity of NCNTs has been attributed to the electronic interaction between

radical intermediates and graphitic planes with high conduction.

Watanabe et al. [82] have investigated the catalytic activity of different N-doped AC samples for

the oxidation of alcohols. Parent and H2O2 treated AC samples were less active while AC treated

with H2O2 followed by NH3 showed better results for the oxidation of BzOH (23% conv) and

cinnamyl alcohol, in both cases the aldehyde was the only product formed. Other alcohols could

not be oxidized by N-doped AC due to the lack of conjugation. Thus, indicating that N-doped

AC containing pyridine, pyrrole and graphite type nitrogen species results in the oxidation of

alcohols by activating the conjugated system and provide active sites for the adsorption and

activation of molecular oxygen. The oxidation was negligible in the presence of radical

scavengers and in the absence of oxygen.


10

Garcia et al. [83] have been reported the catalytic activity of graphene oxide, nitrogen doped GO

and Boron-Nitrogen doped GO for oxidation of hydrocarbon, benzyl alcohol and styrene. The

reactions were carried out in round bottom glass at 120C for different intervals of time. Tetralin

was oxidized into alcohol and ketone by GO with 92% selectivity and 20% conversion using

molecular oxygen in 24 h. 37% conversion was observed for N-GO and 50% conversion with

boron and nitrogen doped GO but in case of (B,N)G the selectivity decreased for alcohol and

ketone because other by products were formed. In case of styrene, (B,N)G was inactive while

NG and BG showed better activity. Cyclooctane conversion was 9% with 90% selectivity for

alcohol/ketone using GO as catalyst. The oxidation reaction proceeded through radical

mechanism. Doping influences the electronic structure of carbon atoms promoting their chemical

reactivity.

Hutchings et al. [84] have investigated activated carbon and graphite supported gold catalysts for

oxidation of glycerol in aqueous NaOH. Under mild reaction conditions (60 °C, 3 h, 3 pO2/bar)

56% of glycerol conversion resulted in a 100% conversion to glyceric acid. Increasing the

pressure of oxygen reduced selectivity towards glyceric acid with other by products being

observed. Although activated carbon alone was inactive for oxidation of glycerol even in

presence of NaOH.

Zhu et al. [85] have investigated activated carbon supported Co3O4 catalyst for oxidation of

benzyl alcohol in the absence of any initiator or promotor. The activity of Co3O4/AC is higher

(81% – 100% conv. at different temperatures) than Co3O4 and AC (18.5% conv) alone. Triazine

framework and oxygen-inert carbon nitride were also used as supports for Co3O4 but resulted in

lower activity. Thus, indicating that activated carbon has crucial role in activating molecular

oxygen during oxidation reactions. The catalytic activity of AC support is also altered by

preparation conditions such as treatment temperature and time.

Wen et al. [86] have reported Co-Ce/AC as an effective catalyst for the wet air oxidation of

phenol. The catalyst was prepared by wet impregnation method and calcined at 700°C. About

71.65% TOC was observed after one hour at 150°C and oxygen pressure of 0.8 MPa. Three

different pathways have been proposed for the WAO of phenol, each of which results in different

intermediates such as catechol, hydroquinone, p-benzoquinone, p-hydroxybenzaldehyde,


11

followed by their final conversion into organic acids and CO2. Co/AC and Ce/AC were also

investigated which showed lower results.

Szymanski et al. [87] have explored the catalytic activity of commercial activated carbon for

dehydration of 2-methylpropane-2-ol in a fix bed flow reactor. AC was oxidized with

concentrated nitric acid and heated at different temperatures for 2 h to elucidate the surface

chemistry influence in the model reaction. Dehydration over strong acidic groups is proposed

when the only product observed was isobutene. Adsorption of bulky alcohol molecules takes

place at acidic groups and the water is removed by cyclic groups formed on the surface of AC

during sample annealing. Oxidized AC desorbed at 523 K demonstrated higher activity, which

decreased at a higher degassing temperature (573 K) due to a decrease in acidic groups.

Rey et al. [88] have investigated the surface activity of three commercial activated carbons for

wet air peroxide oxidation of phenol. AC produced by Merck (CC) and Norit (CN) showed better

activities with relatively different mechanisms. The surface of CC is fairly acidic containing

mainly carboxylic groups, and resulted in the decomposition of H2O2 into inactive oxygen and

water, while phenol was removed by adsorption as no intermediates have been detected for this

carbon material activity. While CN containing anhydride and pyrone groups resulted in a TOC of

91% for phenol. The intermediates detected were catechol, p-benzoquinone and hydroquinone.

The catalytic activity of CN is attributed to its egg-shell type distribution of oxygen groups

which interacts with H2O2 giving OH radicals.

Ramirez et al. [89] have evaluated the effects of surface properties of different commercial

activated carbons used as support for cobalt oxide nanoparticles in the liquid phase oxidation of

benzyl alcohol. AC from different origins, such as G60, RX3, CNR and RB3. Co3O4/G60 and

Co3O4/RX3 showed better catalytic activities (100% conv. and 99% selectivity and 91.1% conv.

and 99% selectivity respectively) in the oxidation reaction as compared to other catalysts. The

former two catalysts have a high Co+3 content and large number of functional groups, while two

other catalysts have the same content of Co+3 species but a smaller number of functional groups,

thus it is clear that the catalytic activity is attributed to the synergistic effects between the surface

chemistry and texture of the ACs and the active phase content. Co3O4 alone resulted in a 48%

conversion and 99% selectivity proving that the excellent activity of Co3O4/G60 and Co3O4/RX3

is due to the dominant role of AC in oxidation reactions.


12

Bach et al. [90] have explored the influence of granular activated carbon (GAC) in the

mineralization of ethylene glycol (EG) along with iron oxide and H2O2. GAC and H2O2 were not

able to catalyze EG because H2O2 is decomposed into oxygen and water by GAC, although EG

is not adsorbed on the surface of GAC. When GAC was combined with iron oxide/H2O2, the

mineralization of EG was enhanced because GAC accelerated the formation of ferrous ions.

However, at high concentrations of GAC, the catalytic activity decreased due to the degradation

of H2O2. Thus, it is obvious that for the optimal catalytic oxidation of EG, an optimal

concentration of GAC is required in the GAC/iron oxide/H2O2 system.

Wu et al. [91] have reported the complete oxidation of BTX over Pt/Activated carbons. ACs

were treated at different temperatures to check their surface properties in the oxidation process.

BTX was completely oxidized at 132°C by Pt/AC800 and 140°C by Pt/AC800HF. Pt/ACs

showed higher activities than that of Pt/Al2O3 (360°C). The adsorption and migration rates of

BTX were higher over the surface of activated carbon. The adsorption of benzene was higher

than toluene and xylene. The effect of humidity was lower due to the hydrophobic surface of the

activated carbons.

Wang et al. [92] reported the catalytic activity of activated carbon supported metals for the

removal of HCN using Mn, Ni, Cu, Co and Fe impregnated on AC. The catalysts were tested for

HCN removal at a temperature range from 100-350°C. N2, NH3, NOx and N2O were detected as

products at 200-300°C. It has been observed that the removal of HCN follows a two-step

pathway, hydrolysis of HCN to give NH3 followed by the oxidation of NH3. Among the tested

catalysts, AC-Cu showed the best catalytic activity with a 48% N2 selectivity being observed at

200-300°C under 0.5% O2 and 10% humidity. The selectivity towards N2 could be increased by

minimizing the amount of NH3, as well as developing appropriate reaction conditions and

catalysts.

Castro et al. [93] have studied the influence of activated carbon support (AC/Fe) for the

oxidative removal of methylene blue and the decomposition of H2O2. A commercial AC from

Merck and an AC prepared from spent coffee grounds were used as support materials for iron

oxide. The catalysts were efficient in the decomposition of H2O2 through a radical mechanism.

About 40% and 50% MB was removed by CAC/Fe and ACK/Fe (spent coffee grounds AC

treated with K2CO3) respectively. However, the removal increased to 92% and 97% in the


13

presence of H2O2 by CAC/Fe and ACK/Fe. The removal of MB occurred through both

adsorption and oxidation processes. The oxidation products were detected after 6, 15 and 24 h

before mineralization.

Oliveira et al. [94] have studied the effect of H2 treatment on the activity of activated carbon in

the oxidation of textile dyes by H2O2. Reducing sites have been developed on the surface of

commercial AC by treating with H2 at 400-800°C. H2O2 was decomposed into HO* and HOO*

most likely through an electron transfer mechanism. The catalysts were tested for their

adsorption contribution using Drimaren Red dye. No discoloration was observed after 4 hours

with any of the samples in the presence of H2O2. Dye removal increased when AC and H2O2

were used, suggesting that oxidation occurred through radical mechanism. The decomposition of

H2O2 was inhibited by phenol followed by hydroquinone and Drimaren Red dye. These organic

compounds participate in a competitive process with decomposition of H2O2 by either adsorption

on the surface of AC or by reacting with radical intermediates such as HO* and HOO*.

Villa et al. [95] have investigated Au-Pd/AC for the oxidation of benzyl alcohol, cinnamyl

alcohol, octanol and 2-octen-1-ol in aqueous solutions. The effect of substrate concentration and

Au-Pd ratio has been explored in terms of TOF and activity. The samples tested were Au10-

Pd90/AC, Au20-Pd80/AC to Au60-Pd40/AC with their activity measured at 60°C and 1.5 atm O2 in

a thermostat glass reactor. Au60-Pd40/AC showed higher activity in case of benzyl alcohol. The

addition of a base showed a prominent effect on activity of catalysts with a higher Au content,

although basic conditions favor over oxidation to carboxylates. In the case of BzOH, selectivity

towards benzaldehyde and benzoic acid strongly depends on the Au/Pd ratio. While in case of

cinnamyl alcohol, the selectivity towards cinnamaldehyde increased with an increase in Au

content even in the presence of a base. The catalytic activity of the materials for the oxidation of

aliphatic alcohols in the presence of a base increased with a high Au content suggesting that Au

acts with a promotor effect in the alloy.

Guo et al. [96] have investigated carbon nanocoils supported Pd nanoparticles (Pd/CNCs) for

photocatalytic Heck coupling reaction. The reactions were carried out using aryl halides and

alkenes in the presence of potassium carbonate and DMF at 40°C. The products were obtained in

70-99% yield in different time intervals. The catalyst was tested for its stability and 92% yield

was obtained after 5th cycle.


14

Heidenreich et al. [97] have reported palladium nanoparticles supported on activated carbon

(Pd/C) for Heck reaction. Different solvents were used in the reaction to check the conversion

and Pd leaching. 98% and 87% conversion were observed in NMP and DMAc respectively for

bromobenzene and styrene while Pd content was the same in solution. Pd was not detected in

toluene but no catalytic activity was observed. Similarly, Pd leaching decreased with increase in

temperature probably due to reprecipitation.

Shendage et al. [98] have reported palladium nanoparticles supported on electronically reduced

graphene oxide for Heck reaction. The reactions were carried out between aryl halides and styrene

and acrylates in the presence of DMF and Et3N at 120°C. The reaction of aryl halides with

electron-donating or electron-withdrawing substituents resulted in excellent yield with olefins.

Styrene required longer reaction time as compared to acrylates. The catalyst showed minimum loss

in activity after 5 cycles.

Satyanarayana et al. [99] have reported palladium nanoparticles supported on carbon

nanomaterials (PdO/GO) for C-C coupling reactions (Suzuki-Miyaura and Glaser). Biphenyl

products were achieved in 90% yield by reacting iodoarenes and aryl-boroic acids in the

presence of PdO/GO catalyst, K2CO3 and DMSO at 120°C in oven-dried Schlenk tube. 1,3

diynes were achieved in fair to good yield from terminal alkynes by Glaser coupling.

PdO/MWCNTs were used as catalyst for the coupling reaction of 2-iodophenol and terminal

alkyne. Benzofuran product was achieved in excellent yield in 24 hours at 120°C following

Sonogashira coupling reaction. The catalyst showed no loss in activity after 5 cycles.

Anasdass et al. [100] have reported palladium nanoparticles decorated reduced graphene oxide

sheets (PdNP/rGO) synthesized by Hummers and Offeman method for Suzuki coupling

reactions. The reactions were carried out using two different aryl halides and phenyl boronic acid

in the presence of different bases. Biaryl product was achieved in 98% yield in the presence of

PdNP/rGO, K2CO3 and ethanol: water system at 180°C in short duration (15 min). The catalyst

resulted in 57% yield after 10 cycles.

Gomes-Ruiz et al. [101] have reported palladium nanoparticles supported on COOH-modified

graphene (G-COOH-Pd-10) for Suzuki-Miyaura coupling reactions. Different boronic acids have

been reacted with 1-bromo-4-florobenzene in DMF/water at a range of temperatures and

different time intervals. Almost complete conversion was observed in the case of 1-bromo-4-


15

florobenzene and 4-florophenylbenzoic acid at 110°C in 48 hours. The catalyst showed 10% loss

in activity after 5th cycle.

Shendage et al. [102] have investigated the catalytic activity of palladium nanoparticles

supported on reduced graphene for Suzuki-Miyaura coupling reaction. The reactions were

carried out in different solvents with different bases but ethanol-water and K2CO3 resulted in

better yield at 80°C. The catalyst efficiently catalyzed variety of substrates. A slight decrease in

activity of catalyst was observed after 7 cycles.

Van Der Voort et al. [103] have reported a saturated metal organic framework V-MIL-47 for the

liquid phase oxidation of cyclohexene. The catalyst consists of vanadium (V+4) and porous

terephthalate framework with octahedral geometry. TBHP was used as oxidant and chloroform

as solvent at 323 K. The four major products formed were cyclohexene oxide, cyclohexane-1,2-

diol, ter-butyl-2-cyclohexenyl-1-peroxide and 2-cyclohexene-1-one with 60% conversion. The

reaction initiated by a linker exchange with TBHP. The catalyst can be regenerated and reused.

Nguyen et al. [104] have reported titanium-functionalized UiO-66 metal organic frameworks for

the oxidation of cyclohexene in acetonitrile at 50°C or either 70°C. The three prepared catalysts

were UiO-66-Tiex, Ti-UiO-66 and UiO-66-Cat-Ti. Ti-UiO-66 showed superior catalytic activity

than the other two catalysts however all of the catalysts favor the allylic oxidation over epoxide.

The products observed were 2-cyclohexene-1-ol, 2-cyclohexene-1-one, cyclohexene oxide and

cyclohexane-1,2-diol. The catalytic activity decreased after three cycles due to leaching of metal.

Jiang et al. [105] have investigated copper-based MOF containing 4,4´-bipyridine linker for

oxidation of cyclohexene in solvent free conditions. The reactions were carried out at 45°C for

15 h using oxygen balloon at atmospheric pressure. 2-Cyclohexene-1-ol, 2-cyclohexene-1-one,

cyclohexene hydroperoxide and cyclohexene oxide were detected as major products. The minor

products were also observed such as cyclohexene dimer, phenol and 2,3-epoxy cyclohexanone

but the amounts of each compound were less than 1%. The allylic oxidation was dominant

reaction and cyclohexene hydroperoxide was produced with 85-90% selectivity at a conversion

of 10%.

Farzaneh et al. [106] have reported Mn-MOF containing benzenetricarboxylate (BTC) for the

oxidation of alkanes and alkenes. Reactions were carried out in CH3CN for 24 h using TBHP as


16

oxidant. Cyclohexene was completely oxidized into corresponding alcohol and ketone products

with 25% and 75% selectivity.

Li et al. [107] have investigated copper, cobalt and nickel containing metal-organic frameworks

for oxidation of cyclohexene in solvent free conditions. Co-MOF catalyzed 32.8% of

cyclohexene into four products while the overall selectivity towards alcohol and ketone was

90.3%. Cu-MOF resulted in a conversion of 20.8% with 80.7% selectivity towards alcohol and

ketone products. All the reactions were carried out for 24 h at 80°C in the presence of oxygen.

Ni-MOF was totally inactive in the model reaction. Co-MOF and Cu-MOF were recycled and no

considerable loss in activity was observed after three cycles.

Brown et al. [108] have reported copper-MOF consisting of 1,2,4,5-benzenetetracarboxylic acid

and 4,4´-bipyridine for oxidation of cyclohexene. A conversion of 64.5% was achieved after 24 h

in the presence of TBHP at 75°C. Epoxidation was dominant reaction giving cyclohexene oxide

(73%) and side products such as cyclohexanone and 2-cyclohexenone.

CHAPTER 03 EXPERIMENTAL

17

3. EXPERIMENTAL

3.1 Materials

3.1.1 Chemicals

All chemical reagents used were purchased commercially and used as received.

3.1.2 Gases

Gases like N2, O2, H2 and Helium were used in this project supplied by BOC Pakistan

Ltd. All these gases were purified by appropriate filters like C.R.S.Inc.202268 and

C.R.S.Inc.202223. Hydrogen gas used for FID was generated by using hydrogen generator

model PGXH2 100 while N2 and O2 were generated by generator Model Parker Domnick hunter.


18

Table 3. 1: Chemicals list used in the present study.

S.NO Chemicals CAS NO Manufacturer

1 Glucose D 50-99-7 Sigma Aldrich

2 Urea 57-13-6 Sigma Aldrich

3 Ethanol 64-17-5 Sigma Aldrich

4 HCl 7647-01-0 Sigma Aldrich

5 H3PO4 7664-38-2 Sigma Aldrich

6 H2SO4 7664-93-9 Sigma Aldrich

7 H3BO4 10043-35-3 Sigma Aldrich

8 NaOH 1310-73-2 Sigma Aldrich

9 CH3COOH 64-19-7 Sigma Aldrich

10 Copper Acetate 142-71-2 Sigma Aldrich

11 BTC 554-95-0 Fischer Scientific

12 Zirconyl Chloride 13520-92-8 Sigma Aldrich

13 NaNO3 7631-99-4 Sigma Aldrich

14 Cyclopentane 287-92-3 Alfa Aesar

15 Cyclohexane 110-82-7 Alfa Aesar

16 Cycloheptane 291-64-5 Alfa Aesar

17 o-Toluidine Blue 92-31-9 Sigma Aldrich


19

3.2 Catalyst Preparation

3.2.1 Activated Carbon (AC1a, b, and c)

The raw materials, Peanut shells (AC1a) / Corncob (AC1b) / Spent Tea Leaves (AC1c)

(200 g) were purified and dried overnight at 105°C in an oven. The sample was soaked in H3PO4

(15%) for 24 h, in a 1:1 ratio (g of peanut shell/mL of acid solution), washed in a modified

Soxhlet apparatus until it reached neutral pH and subsequently carbonized in a tube furnace

(reactor: quartz, diameter of 4 cm, length 50 cm) at 380°C under an inert atmosphere for 1 h. The

precursor weight was reduced to 22 g, after carbonization. The sample was activated with H2O2

in a sonicator (ks 300, KUM SUNG ultrasonic, Korea) for 30 minutes. Finally, the AC was

washed in a modified soxhlet apparatus, dried and sieved (US standard sieves). An additional

thermal treatment of the sample was performed at 580°C with a ramp of 5°C/min and held for 2

h under N2, in order to tune the surface of AC for the desired functional group (quinone) [109].

The weight of the sample was 16.3 g after activation and high temperature treatment, which

shows 91.8% weight loss. The prepared samples (AC I a, b, and c) were used for catalytic

oxidation of cyclohexane to alcohol and ketone with molecular oxygen in well architected glass

reactor.

3.2.2 Catalytic Test of AC (Ia, b and c)

The cyclohexane (12.5 mL) and AC (0.4 g) were loaded to a self-designed double-walled

three-necked batch reactor. The mixture was stirred in the presence of molecular oxygen

(40 mL/min) at 75°C for 14 h. The reaction was also performed in the presence of base NaOH:

0.2 mmol in the same set of reaction parameters. The conversion of cyclohexane to KA oil was

analyzed by gas chromatography (GC, Clarus 580, Perkin Elmer, USA) using cross-linked


20

methyl siloxane capillary column (30 m, 0.32 mm internal diameter, and 0.25 μm film thickness),

connected with flame ionized detector (FID).

3.3 Activated Carbon from Peanut shells (AC II)

Peanut shells were obtained from the local market of Chakdara. The collected shells were

washed with distilled water, dried and grinded to achieve a fine powder. The powder was then

sieved with 170 mesh (≤ 88 µm) and dried at 110oC in an oven for 24 h. After drying, the shells

were pre-carbonized in the tube furnace at about 70°C, and further carbonization was carried out

in the blast furnace at 45°C. The activated carbon was cooled in the desiccator and then soaked

in a H3PO4 solution, stirred for two h, left to sit for 24 h, then washed with distilled water until

neutral pH was reached, and then kept in the oven for drying at 50°C [110]. The dried sample

was sealed in an air tight bottle and used for the oxidation of alcohol.

3.3.1 Catalytic Test of AC II

Benzyl alcohol (10 mL) and AC from peanut shells (0.1 g) were charged into a three

necked batch reactor heated by a heating tape wrapped around the reactor, connected to a digi-

sense thermostat. Reaction was run for 72 h with air at 30°C. The product was determined by

gravimetric method.

A three necked batch reactor, water circulator, condenser, air generator, and magnetic bar were

used for experimental work.

3.4 Activated Carbon from Olive stones (AC III)

Olive stones collected from Talash were washed, dried and finely crushed. The crushed

sample was soaked in 300 mL of a H3PO4 (50%, v/v) solution for 24 h. The acid activated

sample was then treated with 500 mL of a KOH (0.5 M) solution. The sample was washed with


21

distilled water until reaching neutral pH and then carbonized at 280°C using ramp rate of

0.5°C/min and maintaining peak temperature for 2 h under nitrogen flow. The sample was cooled

to room temperature, crushed and stored in an air tight bottle. The sample was investigated for

the removal of toluidine blue from waste water.

3.4.1 Batch Study

Solutions of desired concentrations were prepared by dissolving toluidine blue in deionized

water. AC (III) and toluidine blue solutions were loaded into flasks and placed in a shaker at

desired temperature for specific duration. After experimental run, the adsorption slurry was

filtered. The adsorbate concentration in the filtrate was measured by UV.

3.4.2 Fixed Bed Column Study

In the fixed bed study, a column was packed with AC (III). The internal diameter of column was

1.5 cm and height of packed material was 12 cm. The solution (20 mg/L) was allowed to flow

under gravity. The final concentration of the solution was determined by UV spectrophotometer.

3.5 Synthesis of Zirconium Phosphate by Reflux Method

Zirconyl chloride (10 g) was dispersed in 200 mL phosphoric acid solution (6 M) in a

round bottom flask equipped with a condenser and a magnetic stirrer. The reaction mixture was

stirred for 6 h at 90°C. The product was washed with distilled water and dried in oven at 65°C.

3.5.1 Sodium Ion Exchange

Zirconium Phosphate was dispersed in 0.5 N solution of sodium nitrate. The ZrP/NaNO3

suspension was titrated with 0.1 N NaOH and NaNO3 solution in 1:1 ratio with vigorous stirring.

The mixture was stirred for 12 h when the pH of reaction mixture was 8 (constant). The product

was washed with distilled water and dried in oven at 60°C for 24 h.


22

3.5.2 Synthesis of HKUST-1 on the Surface of ZrP

6 g of NaZrP was dispersed in 100 mL of ethanol in a round bottom flask. Copper

acetate (0.307 mg) solution was added to the NaZrP suspension and stirred for 30 minutes. The

product was washed with ethanol for several times to remove the unreacted metal precursor. The

same product was again dispersed in ethanol and stoichiometric amount of Benzene-

tricarboxylate was added into it and stirred for 30 minutes. The product was washed with ethanol

and dried. One cycle of MOF (HKUST-1) on the surface of NaZrP is complete. For more layers,

the same process was repeated [111].

3.6 Preparation of Carbon Dots

Urea (0.4 g) and glucose (0.25 g) were dissolved in 80 mL distilled water. The solution

was transferred to flask and sealed the flask. In the next step the solution was autoclave for 10 h

at 120°C to brown color product. The mixture was dried for 4-5 days in oven at 120°C till the red

brown color. The sample was dispersed in ethanol and sonicated for 30 minutes. Then the

mixture was transferred to tubes and centrifuged at 10,000 rpm for 20 minutes. The upper liquid

part was discarded and the other part was retained and re-dried in oven. The fluorescence

intensity of the resulting carbon dots (C-Dots) was measured at λex = 370 nm and λem = 450 nm.

3.7 Palladium Nano-Crystals Preparation

3.7.1 Reagent A for octahedral crystals

Polyvinylpyrrolidone (PVP; 105 mg) was mixed with citric acid (CA; 180 mg) in water:

ethanol (5 mL: 3 mL) and the mixture was homogenized through agitation, sonication and

shaking while simultaneously heating the mixture at 80°C in oil bath for 20 minutes.


23

3.7.2 Reagent A for cubic crystals

Polyvinylpyrrolidone (PVP; 105 mg) was mixed with ascorbic acid (AA; 60 mg), KBr (5

mg) and KCl (185 mg) in water (8 mL) and homogenized through agitation, sonication and

shaking while at the same time heated at 80°C in oil bath for 20 min.

3.7.3 Reagent B

Sodium tetrachloropalladate (II) (Na2PdCl4: 57 mg) was dispersed in water (3 mL)

through agitation, sonication and shaking.

3 mL of reagent B was added to reagent A and heated at 80°C for 3 hours under vigorous

stirring. The mixture was diluted to 40 mL with ethanol at room temperature and sonicated for

10 min. Then the mixture was further diluted with 25 mL of acetone/diethyl ether (10 mL: 15

mL) and centrifuged at 11000 rpm for 15 min by a (Combi514R) centrifuge. The nanocrystals

thus prepared were dispersed in 10 mL of water.

3.8 Preparation of Palladium/Carbon Dots

The synthesized carbon dots were used for the adsorptive uptake of palladium nano-cubes and

nano-octahedron. Initially 0.4 ppm solution of Pd nanocrystals was prepared. Then different

concentration solutions were taken in tubes and specified amount of carbon dots was added into

each tube and sonicated for 30 min at 40°C. On one side we successfully studied the quenching

of carbon dots while on the other side obtained the Pd nano-cubes and Pd nano-octahedron

immobilized carbon dots catalysts for Heck reaction.

3.9 Characterization of the Samples

Characterization of the catalysts was performed by XRD, TEM, SEM/EDX, FTIR,

TGA/DTA and BET surface area analyzer.


24

3.10 Experimental Set-up for the Screening of Catalyst

Desired gases like O2, N2 and H2 were used in the study, which were bubbled through the

three necked reactor containing reactant and catalyst. Needle valves were used for maintaining

flow of gases (40 cm3/min) to have specific partial pressures of the gases used for oxidation

reactions. Teflon pipes (quarter inch) with Pyrex glass connections and stopper were used in the

set up as shown in Figure 3.1.

Heating of the reactor was maintained by heating tapes wrapped around the three necked

reactors connected to a temperature controller. The reactor equipped with a condenser while the

temperature of condenser was maintained at 3°C through cold water circulation by water

circulator. Trap placed in Dewar flask containing ice was used to trap the reaction mixture

escaped from condenser. The flow was measured by digited flowmeter.


25

Figure 3. 1: Experimental set up used for oxidation reaction of Cyclohexane.

3.11 Analysis of Reaction Mixture

The reaction mixture was analyzed for the desired products through gravimetric method,

GC, and UV-visible spectrophotometer.

3.12 Gravimetric Method

In this method 2,4-dinitrophenyl hydrazine was used to quantify the ketone in reaction

mixture. To 250 mL of saturated solution (4 mg/cm3) of 2,4-dinitrophenyl hydrazine in 2 N HCl,

5 mL of reaction mixture was added and placed in ice. The precipitate of hydrazine was filtered,

washed and dried at 100°C.


26

3.13 Calculations

Density of cyclohexane = 0. 779 (g/mL)

Molecular weight of cyclohexane = 84.16 (g/mole)

Wt of 10 mL of cyclohexane = 10 (mL) x 0. 779 (g/mL) = 7.79 (g).

No. of moles in 7.79g of cyclohexane = 7.79 (g) /84.16 (g/mole) = 0.0925 (mole)

Molecular weight of cyclohexanone = 98.15(g/ mole)

Molecular weight of hydrazone = 278 (g/mole)

Ketone per mL of reaction mixture = Wppt (g) x 98.15(g/mole) /278 (g/mole)

Moles of ketone formed per cm3 of the reaction mixture = Wketone / 98.15 (g/mole)

Or

Mole percent formation of ketone = Moles of ketone x 100 / moles of CH

3.14 Gas Chromatographic Method

The quantification of major products in the reaction mixture was also performed by GC, model

Clarus 580 PerkinElmer, USA, equipped with cross-linked methyl siloxane capillary column (30

m, 0.32 mm internal diameter and 0.25 µm film thickness) and flame ionization detector. For

G.C. analytical procedure internal standard method was adopted using toluene as internal

standard. Different % of standard sample mixtures of cyclohexanol (ol), cyclohexanone (one) in

cyclohexane and internal standard toluene (1 mL) were prepared for calibration plots as

presented in Figure 3.2. Major products were calculated by equation 1. Specific rate of reaction

was calculated by equation 2, while for average specific rate was determined by equation 3.

Thermodynamic aspect of reaction was calculated by equation 4 and 5.

%mole Conversion = products(moles)

reactants(moles) × 100 1

Specific rate = moles of product

t (sec) ×cat (g) 2


27

Average Specific rate = conv(mole%)

t (sec) ×cat (g) 3

lnk = lnA − Ea/RT 4

lnk = −∆H

RT+

∆S

R 5


28

y = 0.0192x + 0.0101

R² = 0.9989

y = 0.0287x + 0.8056

R² = 0.9828

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50

Peak

rati

o o

f co

mp

on

en

t to

in

tern

al

stan

dard

% Compostion (mole)

Cyclohexanone in Cyclohexane Cyclohexanol in Cyclohexane

Figure 3. 2: Calibration curve for alcohol/ketone in cyclohexane

CHAPTER 04 RESULTS & DISCUSSION

29

4. Results & Discussion:

4.1 Oxidation of Cycloalkane to Alcohol and Ketone

4.1.1. Characterization of the Samples:

The surface morphology of the AC samples was analyzed by SEM. SEM images shows the

materials porous structure, with cross linked channels connecting the internal surface of (AC Ia)

as shown in Figure 4.1. High magnification shows the presence of cavities ranging from 2-10

µm, which provide easy access to internal micro and mesopores [112]. Figure 4.2 shows that

(AC Ib &AC Ic) have no prominent pores in the body. Furthermore, EDX analysis (Figure 4.3)

shows traces of phosphorus and silicon, while carbon and oxygen are still the major components

of (AC I a, b, c).

The BET Surface area of (AC 1a) (1195 m2/g) was investigated by N2 adsorption/desorption at -

196°C, using material with a particle size ranging from 75-106 µm. Chen et al [113] have

reported that the surface area does not play a major role in catalysis in AC samples. Although the

oxygen containing surface functional groups do play a crucial role in catalysis. While the surface

area of (AC Ib = 170 m2/g and AC Ic = 122 m2/g) are too small in comparison to (AC Ia).

Figure 4.4 shows the XRD pattern of (AC I a, b, c). The broad peak observed around 2θ = 24°

corresponding to the reflection of the (002) plane is due to the amorphous structure of AC while

the weak and broad peak at 2θ = 42° is due to the reflection of (100) plane, and is attributed to a

graphite like structure [114, 115].

Thermogravimetric analysis (TGA) was performed going from 25°C to 1000°C. The weight loss

of AC as a function of temperature is presented in Figure 4.5. The first weight loss in AC (10%)

was observed in the range of 28-100°C, and is due to the evaporation of water from the surface.

The second weight loss event (46%), occurring in the range of 100-400°C may be due to the loss

of bulk water and the decomposition of hemicellulose. In this region, the AC was deprived of

carboxylic functional groups [116]. The third and most crucial weight loss (22%, range 400-

550°C)


30

a

a

b

b

Figure 4. 1: SEM images of the (AC Ia) at different magnifications. (a) and (b) represent the

magnified areas marked in large image.

Figure 4. 1: SEM images of the (AC Ib) and (AC Ic).


31

Figure 4. 2: Elemental analysis of (AC I a,b,c).

Figure 4. 3: XRD diffraction pattern of (AC I a,b,c).


32

is attributed to the carbonization process. In this region most of the functional groups were

converted to CO and CO2 [117]. The final weight loss (17%, 550-700°C) is most likely due to

the conversion of AC to a graphite like structure and the disappearance of the ether functional

groups. After 700°C the weight loss flattened out until reaching 1000°C, in this region the

quinonic functional group was still stable [118, 119]. The catalytic activity of AC in the

oxidation reaction mainly depends on the oxygen containing surface functional groups. The

thermal stability of oxygen containing functional groups on the surface of AC at higher

temperatures has been widely investigated [120]. Thus, the presence of quinonic groups on the

surface of AC could play an effective role in catalysis.

The FT-IR spectra, shown in Figure 4.6a, has peaks at 3430 cm-1 (NH stretching), and 1616 cm-1,

(NH bending), 2925 cm-1 (C-H stretching), 2380 cm-1 (CO2 asymmetric stretching), 1516 cm-1

(stretching of N=O), 1386 cm-1 (CH3 bending), 1251 cm-1 (C-C Skeletal), 1082 cm-1 (C-N

stretching) and 820 cm-1 (N-H out plane bending) vibrations. While the spectra in Figure 4.6b

presents peaks at 3772 cm-1 (isolated O-H group), 3677 cm-1 (Si-OH), 3440 cm-1 (OH), 2532 cm-1

2365 cm-1, 1819 cm-1 and 1639 cm-1 (C=O, stretching), 1420 cm-1 (C-O and C=O highly

conjugated stretching), 1009 cm-1 (C-O), and 675 cm-1 (Si-O-Si) vibrations. Figure 4.6c shows

that activated carbon treated at high temperature (580°C) lost most of its oxygen containing

functional groups except quinonic functional group. Figueiredo et al. [121] reported that with

continuous thermal treatment the oxygen containing functional groups decompose to CO and

CO2 at different temperature ranges. Among these functional groups quinones decompose to CO

at high temperatures, 700-1100°C, which is in close agreement with the result of the current

studies.


33

0

25

50

75

100

0 250 500 750 1000

Wt

loss

(%

)

T (˚C)

10 %, T=100 ˚C

46 %, T=400 ˚C

22 %, T=550 ˚C

17 %, T=700 ˚C

Figure 4. 4: Thermogram of (AC Ia) obtained at T=25-1000°C.


34

Figure 4. 5: FTIR spectra of (a) carbonized carbon, (b) activated carbon (H2O2), and (c)

thermally activated carbon.


35

4.1.2 Optimization of reaction parameters

The oxidation of cyclohexane to alcohol and ketone under solvent free conditions was

carried out under different reaction parameters.

4.1.3 Effect of the reaction time

The effect of time was investigated in the range of 2-16 h at a constant temperature of

75°C. Figure 4.7a. shows an almost linear increase in conversion as time progressed, Saturation

occurred after 14 h, while the product selectivity decreased due to the oxidation of the reactant to

adipic acid.

4.1.4. Effect of Partial Pressure and flow of Oxygen

The effect of oxygen partial pressure, in the range of 0-760 Torr, was investigated. The

conversion increased with an increase in pO2 up to 570 Torr, beyond that the conversion

decreased because of the surface saturation with oxygen, as shown in Figure 4.7b. The effect of

oxygen flow rate on the oxidation of cyclohexane to alcohol and ketone was also investigated.

The conversion was observed linearly with oxygen flow rate, as shown in Figure 4.7c. Thus, 40

mL/min was selected as optimal flow rate of oxygen for further reactions as at high flow rate the

selectivity of product declined.

4.1.5. Effect of Temperature

The oxidation of cyclohexane was carried out at different temperatures, from 45-85°C for

14 h. The conversion increased with an increase in temperature linearly up to 75°C and then

decreased at higher temperature. The selectivity of the reaction was strongly dependent on the

temperature and show inverse relationship with temperature as shown in Figure 4.7d.

4.1.6. Effect of catalyst loading

The effect of catalyst loading was determined by adding different amounts of catalyst to

the reaction mixture under the same reaction conditions. Figure 4.7e show that the oxidation of

cyclohexane increased with an increase in catalyst loading. The maximum conversion of CH was

achieved by adding 0.4 g of catalyst at 75°C. Higher catalyst loading decreased the conversion of


36

Figure 4. 6: Reaction parameters (a) time, (b) partial pressure of oxygen, (c) flow of oxygen, (d)

temperature, (e) catalyst loading, and (f) stirring effect


37

cyclohexane, which is likely due to a decrease in the number of collisions of reactant molecules

with the catalyst surface as the catalyst sites are increasing with additional catalyst while the

substrate concentration remains constant.

4.1.7. Effect of Stirring

The effect of stirring on the production of alcohol and ketone showed that the conversion

has a direct relationship with stirring. On the other hand, selectivity rapidly decreased with an

increase in stirring speed (Figure 4.7f). The optimum stirring speed of 1100 rpm was utilized in

further studies. Figure 7a-f show the optimization of reaction parameters, such as temp; 75°C,

time; 4 h, pO2;760 Torr, flow of oxygen; 40 mL/min, catalyst loading; 0.4 g and stirring; 1100

rpm, were used for all experiments or otherwise specified.

4.1.8. Catalytic activity of the catalyst

Figure 4.8a shows the product distribution as a function of oxygen pressure. The liquid

phase oxidation of cyclohexane to cyclohexanol and cyclohexanone over AC in solvent free

conditions in the presence of molecular oxygen shows a maximum conversion of 10.35% and the

productivity=2.14 mmol/g.h in the absence of any initiator, promoter or base. When NaOH was

added under the same reaction conditions, the conversion and productivity were 23.5% and 4.85

mmol/g.h, respectively (Figure 4.8b). The enhanced conversion with NaOH was due to the base

facilitating deprotonation. Furthermore, a conversion of 3.5% and 2.3% was observed in the

presence of air and nitrogen respectively. The oxidation that occurred under nitrogen may be due

to the oxygen functional groups on the surface of the AC. The %conversion of CH without base,

in the presence of a base, with air and nitrogen are given in table 4.1.

On the surface of AC, oxygen containing functional groups are responsible for the

oxidation of cycloalkane to alcohol and ketone [122]. It has previously been reported that the

surface of activated


38

Table 4. 1: CH conversion at different parameters

S.No Reactant Gas Conditions Conversion (%)

1

Cyclohexane

O2

T=75°C, 14 h, pO2=760

Torr, AC

10.35

2

Cyclohexane

O2

T=75°C, 14 h, pO2=760

Torr, AC, NaOH

23.5

3

Cyclohexane

Air

T=75°C, 14 h, AC

3.5

4

Cyclohexane

N2

T=75°C, 14 h, AC

2.3

0

2

4

6

0 95 190 285 380 475 570 665 760

Prod

uct d

istrib

utio

n (

%)

pO2 (Torr)

cyclohexanol cyclohexanone

0

5

10

15

20

25

Oxygen Nitrogen Air Base

% C

on

versio

n

Reaction

ab

Figure 4. 7: (a) Alcohol and Ketone formation as a function of oxygen. And (b) Cycloalkane

to Alcohol and Ketone conversion in oxygen, nitrogen, air, and base.


39

carbon has a strong interaction with molecular oxygen through oxygen containing functional

groups like carbonyl, ketone and quinone [123-126]. Furthermore, Cao et al. [123] showed that

the oxidation reaction occurred through oxygen containing surface functional groups of AC

where these functional groups were regenerated through molecular oxygen. In recent studies it

was seen that among other oxygen containing groups, quinonic groups were the most stable and

a major source for the oxidation of CH. The Fenton-like-mechanisms of the

quinone/hydroquinone system is the most probable route for the propagation of CH oxidation.

The quinone is regenerated from hydroquinone through the continuous bubbling of oxygen

through the reaction mixture [127]. The variety and density of the surface functional groups can

be tuned through chemical/thermal treatment [122]. In the recent studies, generated oxygen

functional groups on the surface of AC were tuned with thermal treatment as shown via TGA.

The activated carbon was treated at high temperature 580°C; therefore, the only existing oxygen

containing functional group would be quinone. Hoffman and coworker [118] showed the

stability of quinonic functional groups up to 800°C. Similarly, Marchon et al. [119] have

reported the stability of quinonic functional groups at high temperature (700°C). As such, the

oxidation of CH to alcohol and ketone follows the mechanism shown in scheme 4.1.

Activated carbon as a catalyst was used in several studies for oxidation reaction of various

alcohol and hydrocarbons. The catalytic activity of the AC in these studies was compared on the

basis of productivity (mmol/g.h) value as presented in Table 4.2. Bao and coworker [120] used

AC for aerobic benzylic oxidation of 2-benzylbenzo[d]imidazoles in reaction conditions;

substrate; 2 mmol, AC; 60 mg, time; 12 h, temp; 80°C and observed maximum productivity of

0.35 mmol/g.h. Similarly, AC was used as a catalyst for oxidation of benzyl alcohol in different

studies with productivity values (0.11 mmol/g.h) and (0.506 mmol/g.h) respectively [128, 129].

Sun et al. [130] reported maximum productivity value (28.8 mmol/g.h) for AC used for oxidation

of CH in acetonitrile with TBHP. Although in the study a high productivity value was observed

but the use of TBHP makes the reaction impractical due to the concern of environmental hazard.

In another study, Watanabe and coworker [122] studied the catalytic activity of activated carbon

for oxidation of cinnamyl alcohol (in ethanol; 5 mL, substrate; 1.1 mmol, AC; 0.1 g,

temperature; 80°C, and time; 15 h). The obtained productivity value was 0.15 mmol/g.h.


40

4.1.9. Activation energy

Figure 4.9 shows the activation energy of the reaction measured for the oxidation of CH

at different temperatures (45-75°C) at standard reaction conditions, substrate; 115.56 mmol, AC;

0.4 g, T; 75°C, time; 14 h, and pO2; 760 Torr. The activation energy was found to be 71.2

kJ/mol. This data is in good agreement with effect of stirring discussed earlier, suggesting that

the reaction was under kinetic control.

In this study, AC Ia catalyzed the oxidation reaction of cyclohexane with productivity of 2.14 in

the absence of any promotor. While productivity enhanced with a base to 4.85. Although AC Ib

and AC Ic were totally inactive in oxidation reaction because of the fact mentioned earlier that

oxidation reaction takes place on the surface of AC involving quinonic functional groups. The

inactivity of AC Ib and AC Ic is related to the poor quinonic functional groups.


41

O

O

OOO

OOHOOH

π conjugation reaction core

OH•

O

OH

O

O•

H•

O

OH

O•

qu

ino

ne

hydr o

quin

one

+2e

-

-2e

-

+

+

Figure 4. 1: Proposed mechanism for oxidation of CH with quinonic group of AC.


42

Table 4. 2: AC-catalyzed organic substrates, with productivity and reaction conditions

S.No Oxidation Reaction Productivity* Reaction Condition Ref

1

Aerobic benzylic oxidation

of 2-

benzylbenzo[d]imidazoles

0.35

Reactant: 2 mmol, AC: 60 mg,

Time: 12 h, Temp: 80°C 120

2 Aerobic oxidation of benzyl

alcohol

0.11

Reactant: 0.184 mmol, AC: 0.1

g, Time: 3 h, Temp:80°C 128

3

Oxidation of benzyl alcohol

0.506

Reactant: 1.1 mmol, AC: 100

mg, Ethanol: 5 cm3, Temp:

80°C, Time: 15 h

129

4 Oxidation of cyclohexane 28.8

Reactant:59 mmol, Acetonitrile:

10 mL, TBHP: 5 mL, O2:30

mL/min, 70°C, 2 h

130

122 5

Oxidation of cinnamyl

alcohol 0.15

Reactant: 1.1 mmol, AC:

100mg, Ethanol: 5 cm3, Temp:

80°C, Time: 15 h

6

Oxidation of CH

2.14 (AC Ia)

0.00 (AC Ib)

0.00 (AC Ic)

Reactant:115.56 mmol, AC: 0.4

g, Temp: 75°C, Time: 14 h,

pO2: 760 Torr This

Study 4.85 (AC Ia)

0.00 (AC Ib)

0.00 (AC Ic)

Reactant:115.56 mmol, AC: 0.4

g, Temp: 75°C, Time: 14 h,

pO2: 760 Torr, NaOH: 0.2

mmol

*Productivity (mmol g−1h−1) = mmol of product

catalyst (g) × time (h)


43

4.1.10. Recycling of catalyst

The activated carbon was used as a catalyst for the oxidation of cyclohexane to KA oil in

the optimized reaction conditions (Reactant; 12.5 mL, AC; 0.4 g, temp; 75°C, time; 14 h, and

pO2; 760 Torr, stirring; 1100 rpm) to investigate life span of the catalyst. The catalyst was used

four times for the oxidation reactions after simply drying in an oven, and the catalytic activity of

activated carbon remained unaltered, as shown in Figure 4.10.

4.1.11. Oxidation of other Cycloalkanes

The AC samples were used as catalysts for oxidation of cyclopentane and cycloheptane as well

at the same set of reaction conditions but no products were detected for any of the reagent.


44

Figure 4. 9: Arrhenius plot of AC-catalyzed conversion of CH to alcohol and ketone

Figure 4. 10: Recycling of AC for cyclohexane to KA oil.


45

4.2. Results and Discussion: Oxidation of Alcohol to Aldehyde by AC II

4.2.1. Characterization of the catalyst (AC II)

4.2.1.1. SEM of The Catalyst

The morphological structure of the activated carbon was analyzed with SEM to explore the

microstructure of the catalyst. The SEM micrographs of activated carbon shows the presence of

channels, that results from chemical activation with acid, as the acid is highly corrosive and

dehydrating in nature (as shown in Figure 4.11). The surface of the activated carbon changed

with temperature and time of activation. Compared to examples from the literature, these SEM

micrographs shows a smooth surface with many orderly pores [131, 132]. The intersection

method was used for measurement of the average particle size from the SEM images. Five spots

were chosen and measured and then the average of the spot sizes was calculated, 146.62 µm,

which also represent an agreement with the sieve analysis.

4.2.1.2. XRD of The Catalyst

On the basis of XRD studies, activated carbons are classified into two types, based on their

graphitizing ability. The non-graphitizing carbons are hard and show a well-developed micro

porous structure due to the formation of strong cross-linking between the neighboring randomly

oriented elementary crystallites. Whereas, graphitizing carbons has weak cross-linking and a less

developed porous structure. From XRD pattern shown in Figure 4.12, it was concluded that the

catalyst is of amorphous nature.

4.2.1.3. FTIR of The Catalyst

FTIR spectra were obtained to detect functional groups on the surface of activated carbon. The

FTIR spectra of the 10% and 25% acid impregnated activated carbons are shown in Figure 4.13

(a and b). Table 4.3 summarizes the wave number and assignment of the main bands observed in

the spectra. The FTIR spectrum of the activated carbons shows O-H bond stretching mixed with

NH2 groups at 3370 cm-1 (intense and broad band). The band at 2920 cm-1 and 2859 cm-1 are

related


46

Figure 4. 11: SEM images of (AC II) impregnated with (a) 10% H3PO4 (b) 15% H3PO4 (c) 20%

H3PO4 (d) 25% H3PO4 (e) 30% H3PO4 (f) 35% H3PO4 (g) 40% H3PO4 at magnification of 500.


47

Figure 4. 12: XRD Pattern of (AC II) impregnated with 10% H3PO4

Figure 4. 13: FTIR of (AC II) impregnated with (a)10% acid and (b)15% acid

to asymmetric and symmetric stretching of CH2 groups, respectively. Scissor bending of the NH2

group can be observed at 1659 cm -1 and 1535 cm-1 (sharp and intense band). The bands at 1224

cm-1, 1149 cm-1 and 1020 cm-1 can be assigned to the carbon C-N stretches of amide or amine


48

groups. The absorption band in the region 750-900 cm-1 can be attributed to P-O, S-O, and

aromatic C-H stretching vibrations. The intense absorption band at 3437 cm-1 as assigned to O-H

bond stretching. The two CH2 group stretching bands at 2924 cm-1 and 2854 cm-1 are assigned to

asymmetric and symmetric stretching of CH2 groups. The sharp band at 1736 cm-1 is assigned to

the carbonyl group of carboxylic acid, and the sharp intense peak observed at 1631 cm-1 is

assignment to the aromatic C=C ring stretching. The bands at 1160 cm-1 and 1098 cm-1 are

assigned to C-O stretching vibrations.

Table 4.3 shows wave number and assignment of principal bands in the FTIR spectra of

activated carbon obtained from peanut shells (PNS). When concentrated H3PO4 is mixed with

PNS at high temperature, it appears to function both as an acid catalyst promoting the bond

cleavage reaction and formation of cross-links via processes such as cyclization and

condensation, and to combine with organic species to form phosphate and polyphosphate bridges

that connect and crosslink biopolymer fragments. Dastgheib and Rockstraw proposed that

various surface acid functional groups (oxygen- and/or phosphorus–containing group) are

developed through the surface oxidation as well as attachment of different oxygen phosphorus

group to the surface, while developing the required porosity. The dehydration of cellulose by

phosphoric acid is similar to the dehydration of alcohols and at higher temperature the

phosphorus oxide act as a Lewis acid and can form C-O-P bond [133].


49

Table 4. 3: Surface functional groups (AC II)

Wave number (cm-1) Assignment

3500-3300 O-H Stretching (intermolecular hydrogen bonded)

2930-2900 C-H Asymmetric, stretching

2800 N-H (amide)

1740 C=O Stretching in esters

1625-1610 C=C Aromatic skeletal stretching

1580-1570 C=C Stretching band

1450-1420 C-H Asym; bending

1375-1317 C-H Asym; and sym; bending

1284-1240 C-O Asym; stretching of aromatic ethers, esters and phenols

1260-1000 C-O in carboxylic acids, alcohols, phenols, and esters or P=O bond in

phosphate esters

700-400 C-C Stretching


50

4.2.2. Oxidation of Alcohol

Activated carbon was selectively able to oxidize benzyl alcohol to benzaldehyde. Gravimetric

analysis revealed that other undesirable products were also formed. A schematic representation

of the reaction is given below:

Scheme 4. 2: Oxidation of benzyl alcohol to benzaldehyde

4.2.3. Optimization of Reaction Conditions

4.2.3.1. Time Study

The oxidation of ROH over activated carbon was carried out from 24-72 h to study the

effect of reaction time on the formation of RCHO and to study the kinetics of oxidation of benzyl

alcohol. This study was carried out at 323K by suspending 0.1 g of catalyst (AC II) in 10 mL of

the reactant and passing oxygen through the reaction mixture with a flow rate of 40 mL/min, at

atmospheric pressure. The results obtained showed that with the increase in reaction time (from

24 h to 72 h) the benzaldehyde formation increases, reaching a maximum value after 72 h

reaction duration, while above this reaction time the benzaldehyde formed either converts to

some other side products or back to the reactants to establish equilibrium. This increase in benzyl

alcohol conversion with time is probably due to the increase in the contact time of reactant with

the active sites of the catalyst surface as well as an increase in contact of the oxidant with the

reactant as the duration of the reaction increases. Figure 4.14 shows that until 72 h of reaction

duration the rate of reaction increases. These results show that the conversion of benzyl alcohol

to benzaldehyde increases linearly with an increase in reaction time (up to 72 h). Therefore, this

reaction follows first order kinetics.

Kinetic analysis of these results using equation


51

Scheme 4. 3: Oxidation of benzyl alcohol to benzaldehyde

t=0 a 0

t=t (a−x) x

dx

dt = k (a − x) (1)

dx

(a−x) = kdt (2)

Integrating equation, we get

∫dx

(a−x) = ∫ kdt

− ln(a − x) = kt + I (3)

Where I is constant of integration in the beginning when t = 0, x = 0 (as no substances have

reacted at the start of the reaction)

Putting this value in equation (3) we get

− ln(a − 0) = k × 0 + I

−lna = I (4)

Or

Substituting this value of “I” in equation (3) we get,

− ln(a − x) = kt + (−𝑙𝑛𝑎) (5)

By rearranging equation 5 we get,

kt = lna − ln(a − x ) (6)


52

As we know that

lna − ln(a − x) = lna

(a−x) (7)

By putting this value of equation (7) in equation (6), and rearranging, we get,

k = 1

tln

a

(a−x) (8)

By re arranging equation (8), we get,

t = 1

kln

a

(a−x) (9)

Where a = initial number of moles of benzyl alcohol

(𝑎 − 𝑥)= remaining number of moles of benzyl alcohol and

K= rate constant

Which indicate first order kinetics i.e the ln a/(a−x) vs (time of reaction) plot is linear. From the

slop of the plot, the value of rate constant could be determined.


53

Figure 4. 14: Plot of ln a/(a−x) vs time (h), oxidation of benzyl alcohol into benzaldehyde

Reaction Conditions: Cat; 0.1 g, vol; 10 mL, Temp; 323K, Air flow; 40 mL/min


54

Figure 4. 15: Plot of mol% Conversion vs Time (h), Oxidation of ROH to RCHO.

Reaction conditions: cat; 0.1 g, vol; 10 mL, temp; 323K, Air flow; 40 mL/min

4.2.3.2. Temperature Effect

The oxidation of benzyl alcohol to benzaldehyde using activated carbon as a catalyst in the liquid

phase was carried out to investigate the effect of temperature on the conversion of ROH to

RCHO in the presences of atmospheric oxygen in the temperature range (303K to 323K) as

shown in Figure 4.16. The study was carried out by adding 0.1 g of catalyst to 10 mL of benzyl

alcohol.


55

The heterogeneous catalytic process in general is based on the following five steps (a)

transportation of benzyl alcohol and oxidant to the surface of catalyst. (b) adsorption of benzyl

alcohol and oxidant on the surface of catalyst. (c) reaction on the active surface of catalyst. (d)

desorption of benzaldehyde from the surface of catalyst. (e) transportation of benzaldehyde and

water molecules away from the catalyst.

Step b, c and d are chemical in nature and combined constitute the catalytic reaction. Step a and e

on the other hand involve no chemical changes. Step 1 is the physical process, where by the

reactant molecules are brought to the surface of the solid catalyst (diffusion process) this is mass

transport or mass transfer. Step 5 is the corresponding diffusion process, in an opposite direction,

so that the products formed are taken away from the catalyst surface. The reaction is said to be

diffusion control or mass transport limited if the catalytic rate of reaction is determined by the

rate of arrival of reaction or removal of product. These types of reactions are usually

characterized by activation energies significantly higher than 25 kJ/mole then rate of the reaction

will depend on the adsorption as well as the chemical step, such reactions are called kinetically

control reactions. In this study, the activation energy of the model reaction is 204 kJ/mole as

shown in Figure 4.17. The main factors that affect the nature of heterogeneous processes include

temperature, pressure of the gaseous reactant, rate of flow and the texture of the catalyst. By

lowering the temperature, the rate of the chemical reaction decreases faster than the rate of

diffusion, which favors a kinetically controlled reaction. Similarly, in cases of uneven texture

and higher porosity, the reactant molecules will not be able to equally access all the sections of

the catalyst and hence the reaction will more likely be kinetically controlled on the surface part

and diffusion controlled inside the pores. A heterogeneous chemical reaction may be kinetically

controlled or diffusion control pores. A heterogeneous chemical reaction may be kinetically

controlled or diffusion controlled or an intermediate between these two.


56

Figure 4. 16: Effect of temperature on the conversion of ROH to RCHO.

Reaction Conditions: Cat; 0.1 g, vol; 10 mL, Time; 72 (h), Air flow; 40 mL/min

Figure 4. 17: Arrhenius plot for activation energy.

Reaction Conditions: Cat; 0.1 g, vol; 10 mL, Time; 73 h, Air flow; 40 mL/min


57

4.2.3.3. Particle Size Study

The liquid phase oxidation of benzyl alcohol to benzaldehyde was carried out using catalysts of

different particle sizes. Figure 4.18 shows that with an increase in the particle size, oxidation of

alcohol increases. This phenomenon may be explained that when particle size is decreased, the

relative pore structure is destroyed. But when there are well developed pores present in the AC,

the reagent molecules could penetrate easily and get involved in the reaction.

Figure 4. 18: Plot for particle size vs % conversion

Reaction conditions: Cat; 0.1 g, vol; 10 mL, T; 323K, Air flow; 40 mL/min


58

4.3 Results and Discussion: Adsorption of Toluidine Blue by Activated Carbon from Olive

Pits (AC III)

4.3.1. Characterization of AC III

The SEM images presented in Figure 4.19 shows the surface morphology of (AC III) with

different magnifications. SEM images reveal the presence of all types of pores on (AC III). The

macropores are larger in size and considered as the part of the external surface of the (AC III).

These smaller pores are responsible for the improved adsorption of TB on (AC III). The pores

with widths <2 nm are referred to as micropores while pores with widths from 2 to 50 nm are

considered mesopores according to IUPAC nomenclature.

In order to find the effect of activation on the surface area of the olive pits, a sample that was not

treated with H3PO4 and KOH was directly subjected to carbonization at 280°C. A surface area

of 180 m2/g was observed, suggesting that the activation before carbonization significantly

increases the surface area of (AC III) and thus can enhance the efficiency of the adsorbent.

Yakout et al. [110] prepared activated carbon from olive pits (ACop) with activation using H3PO4

at different concentrations such as 60, 70 and 80 wt% followed by carbonization at 500°C. The

observed surface areas were 257, 779 and 1,218 m2/g, respectively. In this study, a surface area

of 1209 m2/g was achieved by treating olive pits with 50 w/v% of H3PO4 followed by KOH (0.5

M) and carbonizing at 280°C. This high surface area may be due to the H3PO4 activation

followed by KOH (0.5 M) treatment. Redondo et al. [134] synthesized ACop in alkali media,

KOH, followed by carbonization at 700°C. They observed a surface area of 1815 m2/g

suggesting that KOH significantly enhances the surface area of ACop. Thus, we have achieved

comparatively large surface area at low carbonization temperatures because the acid activation

produces channels on the (AC III) surface whereas the subsequent KOH treatment may

functionalize the acid activated channels.

Figure 4.20 shows the XRD pattern of (AC III). No peaks were observed, which suggest the

amorphous nature of the (AC III). Earlier studies report a similar XRD pattern with no distinctive

peaks in the ACop [135].


59

Figure 4. 19: SEM images of AC III


60

Figure 4. 20: XRD pattern of AC III

Figure 4. 21: FTIR spectra of (AC III)


61

The FTIR spectra of (AC III), treated with H3PO4 (50%) and AC III after TB adsorption are

shown in Figure 4.21. Broad peak at 3,420–3,444 cm-1 indicates the presence of OH group and

water vapor. Further peaks at 2,921 and 2,855 cm-1 and 1,450 cm-1 show aliphatic C–H

stretching in –C–H– and –CH– deformation, respectively. Peaks at 885, 840 and 775 cm-1

confirm the deformation of C–H in differently substituted benzene rings. The band at 1,700 cm-1

refers to the C=O stretching vibration of carbonyl groups. The C–C vibrational band at 1,600–

1,580 cm-1 was attributed to aromatic ring. The peak at 1190-1200 cm-1 indicates the presence of

(P=O) to O-C stretching vibrations (P-O-C hydrogen bonded in aromatic) and POOH bending

vibrations.

4.3.2 Effect of various parameters on percent removal of Toluidine Blue

4.3.2.1 Effect of pH

The initial pH values of the adsorbate solution are one of the important parameters in the

adsorption of an ionic species such as the cationic TB. The changes in pH value affects the

charged density of both adsorbent and adsorbate. Figure 4.22 shows the removal of TB (%) at

different pH values (2.5–9.5) with an initial dye concentration of 20 mg/L and 0.5 g of (AC III).

The adsorption of TB increased with an increase in pH, reaching a maximum removal of 93% at

pH = 9.5. At acidic pH the low adsorption may be due to the competitive accumulation of

protons (H+) on the adsorbent surface as reported elsewhere [136]. The increase in TB adsorption

onto (AC III) at high pH values was due to the electrostatic interaction of the oppositely charged

(AC III) and TB. There are two pKa values (2.4 and 11.6) for toluidine blue [137]. Beyond these

values, TB exhibits positive charges while (AC III) has anionic groups on the surface due to acid

treatment followed by KOH activation. Thus, at high pH the cationic charge density of TB

increases, which results in high adsorption on the adsorbent surface. Alpat et al. [138] and others

also obtained similar enhancement of cationic dyes with an increase in pH [139].

In this study, the TB removal was carried out at an initial solution of pH = 7.5 unless otherwise

specified.

4.3.2.2. Effect of AC III Dose

To investigate the effect of (AC III) loading on the adsorption of TB, a series of experiments

were carried out with different amount of (AC III) ranging from 0.5 to 3.5 g while values of the


62

other variables were constant; dye concentration (20 mg/L), stirring speed = 250 rpm, pH = 7.5

and contact time = 30 min, as shown in Figure 4.23. The removal increased with an increase in

(AC III) dose. This trend was attributed to the (AC III) surface area and the accessibility of more

absorption sites, afterward the surface area was proportional to the adsorbent mass in the solution

[140].

4.3.2.3. Effect of Initial Concentration

Figure. 4.24 shows the adsorption of TB onto AC III as a function of initial dye concentration

and time at experimental conditions temperature = 25°C, pH = 7.5, shaking speed = 250 rpm and

amount of (AC III) = 0.5 g. Adsorption of TB increased as time progressed until equilibrium was

reached at time = 5 min. Moreover, as the system achieved equilibrium by further increase in

time, it is possible that this may be due to the defined mass transfer of TB molecule from the

bulk solution to the outer surface of (AC III) [141, 142]. The percentage of removed TB

decreased with increase in TB concentration, as a high amount of initial dye concentration is

likely to quickly saturate the adsorbent surface.


63

Figure 4. 22: Influence of pH on %Removal of Toluidine Blue by ACIII.

Reaction conditions: 0.5g AC, 25°C, 30 min, C= 20 mg/L, stirring 350 rpm

Figure 4. 83: Effect of amount of AC III on TB removal

Reaction conditions: C= 20 mg/L, 250 rpm, pH=7.5, t=30 min


64

Figure 4. 24: Adsorption of TB at different concentrations

Figure 4. 25: Adsorption of TB as a function of Temperature


65

4.3.3. Thermodynamic parameters

Figure 4.25 shows the effect of temperature on the removal of TB by AC III. The percent

removal of TB decreased from 93% to 49%. This decrease was attributed to the weakening of the

interaction between the active sites of AC III with TB. Thermodynamic parameters reflect the

exothermic adsorption of TB onto AC III, as measured from ΔG°, ΔH° and ΔS°, using Eqs. (2)

and (3):

∆G° = −RT ln (k°) (2)

ln k° = −∆G°

RT = −

∆H°

RT =

∆S°

R (3)

The negative value of ΔG° = –10.88 J suggests that the adsorption process was spontaneous, the

ΔH° = –10.98 J confirms that the adsorption was exothermic, while ΔS° = –3.06 × 10–4 indicates

that the adsorption of TB on AC III was favorable adsorption process [138].

4.3.4. Adsorption kinetics

To measure the kinetics of TB adsorption onto (AC III), pseudo-first-order and pseudo-second-

order kinetics (Eqs. 4 and 5) were applied to experimental data:

ln(qe − qt) = lnqe − kit (4)

t

qt =

1

(𝑘2𝑞𝑒)2+

t

qe (5)

Where qe is the equilibrium amount of TB and qt is the amount of TB adsorbed at equilibrium

and at any time, t, while k1 and k2 are the rate constants for pseudo–first- order and pseudo-

second-order kinetics, respectively. The pseudo-first-order regression value showed poor fitting

(Figure. 4.26 (a)) while the pseudo-second-order equation has better fitting (Figure. 4.26 (b))

with a correlation coefficient value (R2 = 0.9973) that suggests that the TB adsorption onto (AC

III) follow pseudo- second-order kinetics [143].


66

Figure 4. 26 (a): Pseudo-first-order kinetics for TB adsorption on ACIII

Figure 4.26 (b): Pseudo-second-order kinetics for TB adsorption on AC III


67

To determine the rate limiting step in a batch type adsorption process, Weber and Morris’s [144,

145] model was applied to the data:

qt = kit0.5 + C (6)

where qt is the adsorbed amount of TB in mg/g, ki is the diffusion coefficient value in

mg/(gmin½) and t is the time in min.

According to Eq. (6), the curve of qt vs t0.5 should be straight passing through the origin if the

intraparticle diffusion is the rate limiting step. However, in Figure 4.27, the plot is typically

divided into a region with an initial smooth curve combined by a linear plot, which reveals that

diffusion via pores is not a rate limiting step but a boundary control layer was also required in the

adsorption process.

Figure 4. 27: Plot for intraparticle diffusion of TB

4.3.5. Adsorption Isotherm

The most important part of the study was to elucidate the adsorption isotherm for TB adsorption

on AC III. The common isotherms for adsorption such as Langmuir, Freundlich and Temkin

were investigated for TB adsorption on (AC III) [146-148]. According to the Langmuir

adsorption kinetics, adsorption occur at specific homogenous sites on the adsorbent that are all

energetically equivalent. The Langmuir equation can be linearly written as:

Ce

qe=

1

qmaxb+

Ce

qmax (7)


68

where qe is the total adsorbed amount of TB per unit mass of (AC III) at equilibrium, Ce is the

final concentration of TB in a solution at equilibrium, qmax is the maximum adsorption at

monolayer capacity on (AC III) and b is the adsorption constant. The favorability of adsorption

mechanism is shown by dimensionless equilibrium parameter as follows:

RL = 1

(1+b𝐶𝑖) (8)

where Ci is the initial concentration of TB in solution. The value of RL determines isotherm

types, either 0 < RL < 1 which is favorable, RL > 1 which is unfavorable, RL = 1, or linear or RL

= 0, which is irreversible. In this study, the observed RL value was less than one and greater than

zero which confirmed that the adsorption of TB is favorable on (AC III).

The Freundlich equation was employed to examine the experimental data to determine an

explanation for the heterogeneity of the system, the equation is as follows:

lnqe = lnkF + 1

n lnCe (9)

where KF is Freundlich constant associated with an adsorption process such as adsorption

capacity and intensity, respectively. Accordingly, the adsorption data were also subjected to

Temkin adsorption isotherm, the linear form of this equation can be written as:

qe = klnA + klnCe (10)

where k is Temkin binding energy isotherm constant, while A is Temkin isotherm constant. On

the basis of R2 values, the Langmuir model provide a fit at R2 = 0.92 (Figure. 4.28 (a)), smaller

than the regression values for Freundlich at R2 = 0.95 (Figure. 4.28 (b)) and Temkin, which

showed the best fit at R2 = 0.99 (Figure. 4.28 (c)). These results confirm that the mechanism is

monolayer adsorption followed by multilayers formation.

4.3.6. Fixed bed column study

In the fixed bed column study, the maximum amount of dye that was charged into the column

was observed. In the study, the effect of inlet flow rate, height of bed, initial concentration was

not investigated. However, the column study does give a clue that (AC III) prepared from olive

pits can be used efficiently for the removal of TB from textile industry effluent.


69

4.3.7. Fractal analysis

The equation is given as:

lnqe = constant −1

nln(ln Ce) (11)

Ds = 3 − (1

n) (12)

where D is the fractal dimension, Ce is the TB concentration at equilibrium, qe is the adsorption

capacity at equilibrium. A Frenkel–Halsey–Hill plot was constructed for the adsorption of TB on

the surface of (AC III) as presented in Figure. 4.28 (d) The value of fractal dimensions falls at

2.93 while the regression value is R2 = 0.999. The value of the fractal dimension (2.93) gives a

description about the heterogeneity of the surface, structural and geometric properties of the AC

[149]. The value of fractal dimension ≥ 3 represents irregular, rough and porous structure of AC)

while the value of fractal dimension near to 2, suggests the regular, smooth and nonporous

surface of AC [109]. In the present study, the D value is near to 3, which suggests that the

surface of (AC III) is very rough, irregular, and porous in nature.


70

Figure 4. 28: (a) Langmuir Adsorption Isotherm (b) Freundlich Adsorption Isotherm (c) Temkin

Adsorption Isotherm (d) Fractal analysis of AC


71

4.4. Results and Discussion: Carbon Dots Synthesis, Quenching and Catalysis

4.4.1. Fluorescence Spectra of Carbon Dots

The carbon dots prepared from urea and glucose show strong fluorescence at λ=450 nm with

excitation at λ =370 nm. The results are given in table 4.4 and shown in Figure 4.29. The spectra

at lower wavelength is the excitation spectra and that at higher wavelength is the emission

spectra. The high fluorescence intensity at concentration of 20 ppm make the carbon dots

promising to be used for quenching studies.

4.4.2. Effect of time of autoclave on the formation of carbon dots

The effect of autoclave time on the fluorescence intensity and the consequent yield of

carbon dot was investigated by changing time at a difference of 5 hr. The results of FI for two

different concentrations is given in table 4.5. These results show that the optimum autoclave time

for carbon dots is 10 hr both for lower and higher concentrations.

4.4.3. Effect of time on the stability of carbon dots

The stability of different concentrations of carbon dots was followed for 6 min each and no

substantial variation in the fluorescence intensity was observed which confirms the absence of

any side reaction (Figure 4.30).


72

Table 4. 4: Fluorescence Spectra of Carbon dots

Wavelength (nm) FI Wavelength (nm) FI

220.0 99.296 390.0 187.399

230.0 142.893 400.0 140.908

240.0 137.478 410.0 110.342

250.0 146.702 420.0 76.991

260.0 154.493 430.0 51.270

270.0 150.908 440.0 38.685

280.0 145.733 450.0 664.629

290.0 143.860 460.0 16.837

300.0 142.785 470.0 5.591

310.0 149.657 480.0 6.089

320.0 170.818 490.0 6.899

330.0 196.515 500.0 8.850

340.0 212.090 510.0 11.135

350.0 226.457 520.0 14.695

360.0 234.744 530.0 20.200

370.0 236.838 540.0 28.406

380.0 226.776


73

Figure 4. 29: Fluorescence Spectra of Carbon Dots.


74

Table 4. 5: Effect of autoclave time on the fluorescence intensity of Carbon Dots

Time (hr.) Concentration (ppm) FI

5

2.5 59.109

10 235.450

10

2.5 191.178

10 999.999

15

2.5 46.242

10 158.439

Figure 4. 309: Effect of time on the stability of Carbon dots


75

4.4.4. Effect of pH on the formation of carbon dots

As given in table 4.6 and shown in Figure 4.31, under mild acidic conditions the FI of

carbon dot is maximum. Under neutral condition the carbon dots show minimum FI which goes

on increasing when the medium become more basic. This further confirms that the carbon dot is

stable under mild acidic or basic conditions.


76

Table 4. 6: Effect of pH on the fluorescence intensity of Carbon dots

pH FI

2 152.186

4 175.325

6 158.813

8 160.112

10 164.854

Figure 4. 31: Effect of pH on the fluorescence intensity of Carbon dots


77

4.4.5. Effect of concentration of carbon dots on their yield

The FI vs concentration data is given in table 4.7 and the graphical representation is

shown in Figure 4.32. These results show that the FI of carbon dots increases linearly with

increase in concentration up to an optimum limit of 10 ppm. Beyond the optimum limits, there is

a drastic increase in the FI of carbon dots, which may be due to some sort of interactions among

the carbon dots particles that leads to emission higher than expected.

Table 4. 7: Effect of concentration of Carbon dots on the fluorescence intensity (Linearity study)

Concentration (ppm) FI

1 39.717

2 83.796

3 113.216

5 182.967

8 278.517

9 326.103

10 372.69

20 671.084

30 957.559

40 1015.824


78

Figure 4. 32: Effect of concentration of carbon dots on fluorescence intensity (linearity study)

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35 40 45

Flu

ore

scen

ce I

nte

nsi

ty

Concentration (ppm)


79

4.4.6. Characterization of Pd nanocrystals

Pd nanocrystals were characterized by TEM and XRD. TEM images of the Pd nanocrystals

presented in Figure 4.33 (a, b), shows more than 70% of octahedral nanocrystals with size

ranging from 6 to 8 nm. TEM images of Pd nanocubes as prepared are given in Figure. 4.34 (a,

b), which present cubic crystal shapes with similar edge lengths although (~<10%) some other

shaped particles were observed with crystal size ~8 nm. Figure 4.35 shows the diffraction

patterns of octahedral Pd nanocrystals. As expected, octahedral show a strong (111) peak

compared to that of the (200) peak because of their predominant {111} surfaces. The diffraction

peaks of Pd cubes show close agreement with the fcc crystalline structure of bulk Pd (JCPDS

card No. 46-1043), consistent with {111}, {200}, {220}, {311}, and {222} planes. The intensity

ratio of (111) to (200) peak in Pd nanocubes decreases slightly as compared to the standard value

calculated from JCPDS data, indicating that the reflection of {100} planes dominates in Pd

nanocubes as shown in Figure 4.36.

6nm

Figure 4. 33: TEM images of octahedral nanocrystal of Pd with scale bar: (a) 50 nm and (b)100

nm.


80

8nm

Figure 4. 34: TEM images of Pd nanocubes with scale bar: (a) 50 nm and (b)100 nm.

50

150

250

350

450

550

650

30 40 50 60 70 80 90

Inte

nsi

ty (

a.u

)

2θ (degree)

Figure 4. 35: XRD diffraction peaks of octahedral nanocrystals of Pd.


81

0

200

400

600

800

1000

1200

30 40 50 60 70 80 90

Inte

nsi

ty (

a.u

)

2θ (degree)

Figure 4. 36: XRD diffraction peaks of Pd nanocubes.


82

4.4.7. Palladium nanocrystals Uptake by Carbon Dots

The synthesized Carbon dots were investigated for quenching. Palladium nanocrystals such as Pd

nanocubes and Pd octahedron were used in the study. Three types of carbon dots prepared at 5 h,

10 h and 15 h autoclave time were used for the adsorptive quenching of Pd nanocrystals as

shown in Figure 4.37 (a,b,c). Initially 0.4 ppm solution of Pd nanocubes and octahedron were

prepared. The fluorescence Intensity of the solution was 5.852 and 0.164 nm, respectively and

maximum molecular excitation was 372 nm for both of the Pd nanocrystals solutions. It was

observed that the best choice for the adsorptive quenching of Pd nanocrystals was 10 h autoclave

carbon dot. While the octahedral nanocrystals of Pd were more adsorbed as compare to Pd

nanocubes at all of the carbon dots samples. The adsorptive quenching followed Langmuir type

adsorption model and first order kinetics because the fluorescence intensity linearly decreased

with increase of concentration similarly the percent uptake was linearly increased with increase

of concentration which confirm that the data obey Langmuir type adsorption model. Figure 4.37

(a,b,c) shows the comparative adsorption of Pd nanocubes and Pd octahedron on carbon dots.

Which reveal that octahedron nanocrystals of Pd were more adsorbed as compare to Pd

nanocubes.

4.4.8. Heck Reaction

The Pd nanocrystals adsorbed on carbon dots were used for catalyzing Heck reaction. It was

found that Pd octahedron nanocrystals were more efficient than Pd nanocubes in catalyzing Heck

reaction. The yield of product increased with catalyst weight. The highest yield was 22.5% and

71.5% respectively when Pd-nanocubes/Cdots (25 mg) and Pd-nanooctahedron/Cdots (25 mg)

were used as catalysts. The results are shown in Figure 4.38 and Pd/C catalyzed Heck reactions

are listed in Table 4.8.


83

0

10

20

30

40

50

60

70

80

90

0 0.1 0.2 0.3 0.4 0.5 0.6

Up

tak

e (%

)

Pd Conc (ppm)

Pd nanocubes Pd nano-octahedron

Figure 4. 37 (a): Adsorptive quenching of Carbon Dots prepared at 5 h autoclave time

0

20

40

60

80

100

0 0.1 0.2 0.3 0.4 0.5 0.6

Up

tak

e (%

)

Pd Conc (ppm)

Pd nano cubes Pd nano octahedron

Figure 4.37 (b): Adsorptive quenching of Carbon Dots prepared at 10 h autoclave time


84

0

5

10

15

20

25

30

35

0 0.1 0.2 0.3 0.4 0.5 0.6

Up

tak

e (%

)

Pd Conc (ppm)

Pd nanocubes Pd nano-octahedron

Figure 4.37 (c): Adsorptive quenching of Carbon Dots prepared at 15 h autoclave time


85

Pd nano Cubes

Pd nano octahedron

0

20

40

60

80

10 15 20 25

Conv

(m

ole

%)

Pd/CDs (mg)

Figure 4. 38: Heck reaction catalyzed by Pd nanocrystals/CDs


86

Table 4. 8: Palladium catalyzed Heck reactions

S.

No

Reactant 1 Reactant 2 Conditions %Yield Reference

1

Aryl Iodide

Methyl

acrylate

T = 120°C, 1 h, K2CO3, DMF,

Pd/Fe3O4@C

100

46

2

Aryl Iodide

Styrene T = 40°C, 12 h, K2CO3, H2O,

Pd@C-dots-PVP

95

47

3

Bromobenzene

Styrene

T=140°C, 20 h, DMAc,

NaOAc, Pd/C

91

97

4

Aryl Iodide

Methyl

acrylate

T=140°C, 0.5 h, TEA/NaCO3,

Pd/C

100

150

5

Bromobenzene

Styrene

T=80°C, DMF, K2CO3, 4 h,

Pd-nanocubes/C-dots

22.5

This Study

6

Bromobenzene

Styrene

T=80°C, DMF, K2CO3, 4 h,

Pd-nanooctahedrons/C-dots

71.5

This Study


87

4.5. Results and Discussion: Oxidation of Cyclohexene by Metal-Organic Frameworks

Hybrid

4.5.1. Characterization of MOF/ZrP

The XRD reveals that there is a distinct peak at 10.75° for ZrP. The progressive development of

MOF layers on the surface of ZrP gave rise to many new peaks. With four layers of MOF

deposition, the peak at 10.75° disappears which indicates the successive growth of MOF on the

surface as shown in Figure 4.39. The characteristic peak of ZrP did not shift with the deposition

of MOF suggesting that the Cu ions have exchanged only the surface protons and sodium ions

from NaZrP. In order to prevent the penetration of Cu ions into the inter layers of zirconium

phosphate, sodium exchanged ZrP was used as support. There is a distinct peak for MOF at 8.0°

with six layers of deposition. Figure 4.40, shows the microstructure of ZrP and HKUST-1 on the

surface of ZrP. With the increase in the layers of HKUST-1, the grain size gradually increased.

Initially, a lower concentration of reactants resulted in the formation of a layer of minor HKUST-

1 dispersed uniformly over the surface of ZrP. The smooth morphology of HKUST-1/ZrP

revealed the retention of shape of parent support material and uniformed growth of HKUST-1on

the surface of ZrP [111].


88

10 20 30 40

0

200

400

600

800

1000

Inte

nsity (

A.U

)

Angle (2)

0 10 20 30 40

0

100

200

300

400

500

600

700

Inte

nsity (

A.U

)

Angle (2)

a

b

Figure 4. 39: XRD pattern of ZrP and MOF/ZrP with 10 layers


89

4 layers

2 layers

6 layers

Reflux ZrP

Figure 4. 40: SEM images of ZrP, 2 Layers of MOF/ZrP, 4 Layers of MOF/ZrP and 6 Layers of

MOF/ZrP

TGA curve reveals 12% weight loss with increase in temperature as shown in Figure 4.41 (I).

The first weight loss is due to dehydration of the ZrP and residual solvent up to 150°C. The

second weight loss beyond 150°C to 450°C is due to the decomposition of ligand.

Figure 4.41 (II) exhibits that two bands at 3595 cm-1 and 3502 cm-1 are attributed to O-H

stretching. The bands at 1624 cm-1 and 1215 cm-1 are due to the carboxylate group of BTC

ligand.


90

Figure 4. 41: (I) TGA of ZrP and MOF/ZrP (II) FTIR spectrum of MOF/ZrP (III) Surface area

of ZrP and different layers of MOF/ZrP (IV) Pore Volume of ZrP and different layers of

MOF/ZrP


91

The band at 952 cm-1 suggests the condensation of P-OH of ZrP. The band at 609 cm-1 is due to

the vibrations of Zr-O.

Figure 4.41 (III, IV) and Figure 4.42 shows the surface area of ZrP and ZrP with different MOF

layers. These samples were activated at 100⁰C for 12 h and N2 was adsorbed at 77k using

Micromeritics ASAP 2420 system. The surface area of support material that is ZrP is 35 m2/g.

After deposition of 2 layers of MOF, the pores of ZrP are covered by MOF so the surface area is

reduced to 23.75 m2/g. Further deposition of MOF layers resulted in increase in surface area

from 71.62 m2/g for ZrP-MOF with 4 layers to 285 m2/g for ZrP-MOF with 10 layers, given in

Table 4.9.


92

Table 4. 9: Surface area of MOF/ZrP with different number of Layers

S.No Samples Surface area (m2/g)

1 ZrP

35.08

2 MOF/ZrP

2 Layers

23.76

3 MOF/ZrP

4 Layers

71.63

4 MOF/ZrP

6 Layers

192

5 MOF/ZrP

10 Layers

285


93

Figure 4. 42: N2 Adsorption/Desorption isotherm at 77K for MOF/ZrP with 2, 4, 6 and 10

Layers of MOF


94

4.5.2. DFT Study of HKUST-1

The cell structure of HKUST-1 shown in Figure 4.43, is used to study the chemical bonding and

electronic properties. The calculations for the chemical bonding and electronic properties of the

HKUST-1 have been performed using full potential linearized augmented plan waves

(FPLAPW) methods [151] in the frame work of DFT using WEIN2K code [152]. The exchange-

correlation energies for all the systems are treated by generalized gradient approximation (GGA-

sol) [153]. In FPLAPW technique the unit cell is separated in to two regions, the interstitial

regions and the muffin-tin spheres region taking the muffin-tin radii (RMT) such that no charge

leakages occur. Inside the muffin-tin spheres the wave function is expended in the spherical

harmonics by taking lmax = 10 the maximum value of angular momentum and the magnitude of

the largest vector in the charge density Fourier expansion is Gmax = 12 Ry1/2. Whereas outside the

sphere (interstitial region) it is expanded in plane wave basis and cut-off value of Kmax = 6/RMT is

taken. The convergence is ensured for less than 1 mRy/a.u. and 1000 k-points is used in the

irreducible part of the Brillouin zone.

Figure 4. 43: Structure of HKUST-1

Chemical bonding between the constituent elements in HKUST-1 is visualized through electron

charge density for the (100) and (110) crystallographic plane shown in Figure 4.44. It is obvious

that there is a covalent bond between the Cu and O due to overlapping of charge densities in both

(100) and (110) plane. The charge density of OW is spherical which confirms the ionic bond

between OW and Cu atom in the (100) plane while the bond between C and H atom is also


95

covalent, shown in the (110) plane. On the other hand, electro-negativity of the H, C, O and Cu

are 2.20, 2.55, 3.44 and 1.90 (Puling scale) [154, 155] respectively whose electronegative

difference is 0.35 and 1.54 less than 1.67 [156] also confirms covalent bond between C-H and

Cu-O.

Figure 4. 44: Electronic band structure of the HKUST-1

Most of the physical properties of a compound are either directly or indirectly related with the

electronic band structures. Different compounds have different kinds of band structures due to

which every compound has unique electronic properties. The electronic band structure dispersion

in K-space along the high symmetry direction in the irreducible Brillouin Zone, are calculated

using self-consistent field (SCF) calculations and plotted in Figure 4.45. The figure shows that

the valance band maxima is pulled by the conduction band minima to cross the Fermi level

makes the material metallic. This metallicity in the materials is due to the hybridization between

Cu via O and covalent bond between H-C as in SrFeO3: Co [156].


96

Figure 4. 45: Electron charge densities of the HKUST-1 in (100) and in (110) crystallographic

directions

4.5.3. Oxidation of Cyclohexene

Figure 4.46 shows the product distribution and % conversion as the function of different number

of layers of ZrP-MOF under the experimental conditions: 10mL cyclohexene with 100mg of

catalyst at 80°C in 24 h under oxygen atmosphere. Aerobic oxidation of cyclohexene in solvent

free condition yielded 2-cyclohexene-1-ol and 2-cyclohexene-1-one and also cyclohexene oxide

while other minor products such as cyclohexene dimer, cyclohexanol and cyclohexanone were

also detected as reported elsewhere for Cu catalysts [157]. Cyclohexene oxide formation is a

minor reaction resulting from oxidation of C=C bond while the allylic oxidation product, 2-

cyclohexen-1-one, was dominant in all the reactions. The selectivity towards cyclohexanone was

53.6%, 44.5%, 64.9%, 35.8% and 47.9% with 2, 4, 6, 8 and 10 layers of MOF-ZrP, respectively.

Similarly, the selectivity towards cyclohexanol was 41.1%, 39.1%, 32.9%, 35.3% and 41.6%

respectively. In our case the high %conversion (93.7% and 93.6%) was observed with 2 and 6

layers of MOF-ZrP. Although the product distribution shows much fluctuation with the layers of

MOF. Figure 4.46 reflects that the selectivity of catalyst towards major products with ten layers

of MOF was higher as compared to others where only 0.7% by-products were formed.


97

Selectivity is very difficult for oxidation of cyclohexene due to the existence of two active sites,

the allylic C-H bond and C=C

Scheme 4. 4: Oxidation of cyclohexene

Reaction Conditions: Reagent; 10 mL, Catalyst; 100 mg, t; 24 h, T; 80°C.

bond. When C=C bond is oxidized, cyclohexene oxide, cyclohexanol, cyclohexanone and

cyclohexanediol will be produced. As the C-H bond is oxidized, 2-cyclohexene-1-ol, 2-

cyclohexene-1-one and cyclohexene hydroperoxide will be formed [158]. It was observed that

the abstraction of allylic hydrogen to give allylic oxidation products is more favorable with Cu-

MOF catalyst as compare to the oxidation of C=C bond as reported elsewhere [159].

No doubt, ZrP-MOF proved excellent catalytic activity for cyclohexene oxidation but we did not

observe any catalytic activity for oxidation of cyclopentane, cyclohexane and cycloheptane at the

same set of reaction parameters. The catalytic activity of some catalysts for cyclohexene as well

as results of current studies are given in the Table 4.10.


98

Figure 4. 46: Conversion (%) and product distribution (%) with different number of MOF layers

on ZrP

Table 4. 10: Oxidation of Cyclohexene reported in Literature and results from current study

S.No Catalyst Conditions Conversion

(%)

Selectivity(%)

Ox, Ol, One*

References

1 Mn(BTC) Cyclohexene, TBHP,

24 h, CH3CN

100

0, 25, 75

107

2 Cu-Nb2O5 Cyclohexene, TBHP,

60°C, 12 h, ACN

14

1.8, 2.2, 80

160

3 Cu3(BTC)2 Cyclohexene, TBHP,

50°C, 20h,

50

60, 0, 40

161

4 HKUST-1/ZrP Cyclohexene, O2,

80°C, 24 h

92

4.3, 41.1, 53.6

This Study

5 HKUST-1/ZrP Cyclopentane, O2,

80°C, 24 h,

0

0

This Study

6 HKUST-1/ZrP Cyclohexane, O2,

50°C, 24 h

0

0

This Study

7 HKUST-1/ZrP Cycloheptane, O2,

80°C, 24 h,

0

0

This Study

Ox; cyclohexene oxide, Ol; cyclohexenol, One; cyclohexenone

REFERENCES

99

Conclusions

(Activated carbon AC1a,b,c) was synthesized by chemothermal process and used for solvent-

free oxidation of cyclohexane at low temperature with molecular oxygen. Only (AC1a) was

successfully tuned with thermal treatment for development of quinonic functional groups on the

surface. Optimal reaction parameters were set up as follows: reactant, 115.56 mmol; AC, 0.5 g,

temp, 75°C; time, 14 hours; pO2, 760 Torr; stirring, importance of current study. The catalyst

was reused several times which shows durability of the catalyst. The mechanistic proposals of

the studies show that the quinonic functional group is the best reaction core for oxidation of

cyclohexane with regenerative nature with molecular oxygen. The (ACIa) was found as truly

heterogeneous catalyst with extended lifespan. Similarly, the effect of activating agent

concentration on the pore structure and surface chemistry of (ACII) with chemical activation

method using phosphoric acid as the activation agent. The catalyst (ACII) was prepared and

characterized by SEM, XRD and FTIR. SEM technique was employed to observe the surface

physical morphology of the (ACII). According to the SEM micrographs the raw material before

chemical activation does not have porous surface, while the external surface of the chemically

activated carbon is rich with pores. The FTIR analysis results indicate surface functional group.

The application of activated carbon for liquid phase solvent free oxidation of benzyl alcohol to

benzaldehyde under mild conditions revealed that the catalyst possess catalytic efficiency for the

reaction. The activation energy of the reaction was 204 kJ/mole which indicates that the process

is kinetic- controlled and proceed with first order kinetics. The catalyst is recyclable with no loss

of activity for five runs.

ACIII with surface area 1,209 m2/g and total pore volume 0.78 cm3/g was utilized for the

eradication of TB from aqueous medium. The fractal analysis revealed that the surface of

(ACIII) was porous. The maximum adsorption of TB on (ACIII) was 83% at optimal conditions

pH = 7.5, concentration of TB = 20 mg/L, dose of adsorbent = 3.5 g/L, time = 5 min and

temperature = 298 K. The adsorption of TB on (ACIII) followed pseudo-second-order kinetics

with regression value of (R2 = 0.99) and proceeds with Temkin adsorption isotherm (R2 = 0.99).

Fixed bed column studies show that (ACIII) was a potent adsorbent material for TB adsorption

from the aqueous medium.

REFERENCES

100

Green fluorescent carbon dots were prepared with maximum fluorescent intensity of 664 at

λ=450 nm and used for quenching of palladium nanocrystals (control size (6-8 nm) and shape

(cubes and octahedron). The adsorptive uptake of Pd-nano octahedron was more favorable than

Pd-nanocubes. Further, Pd/C-dots was used as catalyst for Heck reaction with magnificent yield.

However, the Pd nanocubes/C-dots was not so efficient for Heck reaction in comparison with Pd

octahedron nanocrystals/C-dots under the same set of reaction parameters.

The surface grafted MOF was successfully synthesized via layer by layer growth of MOF on

zirconium phosphate (ZrP) which shows prominent porosity, high surface area and good

catalytic activity for cyclohexene oxidation. The major products for cyclohexene oxidation with

oxygen at mild reaction conditions were cyclohexenol and cyclohexenone with less than one

percent by-products. DFT studies confirmed that the copper present on the edges of the MOF is

responsible for the oxidation of cyclohexene. These active sites (Cu2+) disappeared on

dehydrating the MOF with loss of the catalytic activity for oxidation of cyclohexene. Further the

increase of layers of MOF on the ZrP facilitate the mobility of electrons which enhances the

catalytic activity of the catalyst with progressive growth of layers.

Future Prospective: The catalysts (activated carbon and MOFs) investigated for oxidation

reactions in this thesis also has applicability for carbon dioxide capturing and need further

investigation.

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